Search

The disk-outflow connection plays a key role in extracting excess angular momentum from a forming protostar. We have previously reported the discovery of a small molecular outflow from the edge-on T Tauri star in the Bok globule CB26 that shows a peculiar velocity pattern, reminiscent of an outflow that corotates with the disk. We report new, high-resolution mm-interferometric observations of CB26 with the aim of revealing the morphology and kinematics of the outflow at the disk-outflow interface. The IRAM PdBI was used to observe CO(2-1) at 1.3mm with a resolution of 0.5". Using a physical model of the disk, which was derived from the dust emission, we employed chemo-dynamical modeling combined with line radiative transfer to constrain kinematic parameters and to construct a model of the CO emission from the disk that allowed us to separate the emission of the disk from that of the outflow. Our observations confirm the disk-wind nature of the rotating molecular outflow from CB26. The new high-resolution data reveal an X-shaped morphology of the CO emission close to the disk, and vertical streaks extending from the disk surface with a small half-opening angle of ~7deg, which can be traced out to vertical heights of ~500au. We interpret this emission as the combination of the disk atmosphere and a well-collimated disk wind, which we trace down to vertical heights of 40au, where it is launched from the surface of the flared disk at radii of 20-45au. The observed CO outflow has a total momentum flux of 1e-5 Msun km/s/yr, which is nearly three orders of magnitude larger than the maximum thrust that can be provided by the luminosity of the central star. We conclude that photoevaporation cannot be the main driving mechanism for this outflow, but it must be predominantly an MHD disk wind. It is thus far the best-resolved rotating disk wind observed to be launched from a circumstellar disk., Comment: Accepted by A&A, 25 pages, 19 figures

Aiming to detect planetary companions to young stars with debris disks via the radial velocity method, we observed HD114082 during April 2018 - August 2022 as one of the targets of our RVSPY program (Radial Velocity Survey for Planets around Young stars). We used the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs). Additionally, we analyzed archival HARPS spectra and TESS photometric data. We used the CERES, CERES++ and SERVAL pipelines to derive RVs and activity indicators and ExoStriker for the independent and combined analysis of the RVs and TESS photometry. We report the discovery of a warm super-Jovian companion around HD114082 based on a 109.8$\pm$0.4 day signal in the combined RV data from FEROS and HARPS, and on one transit event in the TESS photometry. The best-fit model indicates a 8.0$\pm$1.0 Mjup companion with a radius of 1.00$\pm$0.03 Rjup in an orbit with a semi-major axis of 0.51$\pm$0.01 au and an eccentricity of 0.4$\pm$0.04. The companions orbit is in agreement with the known near edge-on debris disk located at about 28 au. HD114082b is possibly the youngest (15$\pm$6 Myr), and one of only three younger than 100 Myr giant planetary companions for which both their mass and radius have been determined observationally. It is probably the first properly model-constraining giant planet that allows distinguishing between hot and cold-start models. It is significantly more compatible with the cold-start model., Comment: 10 pages, 9 figures, 5 tables; Accepted for publication in A&A Letters

We introduce our Radial Velocity Survey for Planets around Young stars (RVSPY), characterise our target stars, and search for substellar companions at orbital separations smaller than a few au from the host star. We use the FEROS spectrograph to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs) of 111 stars most of which are surrounded by debris discs. Our target stars have spectral types between early F and late K, a median age of 400 Myr, and a median distance of 45 pc. We determine for all target stars their basic stellar parameters and present the results of the high-cadence RV survey and activity characterization. We achieve a median single-measurement RV precision of 6 m/s and derive the short-term intrinsic RV scatter of our targets (median 22 m/s), which is mostly caused by stellar activity and decays with age from >100 m/s at <20 Myr to <20 m/s at >500 Myr. We discover six previously unknown close companions with orbital periods between 10 and 100 days, three of which are low-mass stars, and three are in the brown dwarf mass regime. We detect no hot companion with an orbital period <10 days down to a median mass limit of ~1 M_Jup for stars younger than 500 Myr, which is still compatible with the established occurrence rate of such companions around main-sequence stars. We find significant RV periodicities between 1.3 and 4.5 days for 14 stars, which are, however, all caused by rotational modulation due to starspots. We also analyse the TESS photometric time series data and find significant periodicities for most of the stars. For 11 stars, the photometric periods are also clearly detected in the RV data. We also derive stellar rotation periods ranging from 1 to 10 days for 91 stars, mostly from TESS data. From the intrinsic activity-related short-term RV jitter, we derive the expected mass-detection thresholds for longer-period companions., Comment: 24 pages, 14 figures, 4 tables; Accepted for publication in A&A

Young and magnetically active low-mass stars often exhibit non-thermal coronal radio emission due to the gyration of electrons in their magnetized chromospheres. This emission is easily detectable at centimeter wavelengths with the current sensitivity of large radio interferometers like the VLA. With the aim of identifying nearby stars adequate for future accurate radio astrometric monitoring using Very Long Baseline Interferometry (VLBI), we have used the VLA in its B\, configuration to search for radio emission at \mbox{$\nu \simeq 6$\,GHz} \mbox{($\lambda \simeq 5$\,cm)} toward a sample of 170 nearby ($<$130\,pc) mostly young (5\,--\,500\,Myr) stars of spectral types between F4 and M2. At our mean $3\sigma$ detection limit of $\simeq$\,50\,$\mu$Jy, we identify 31 young stars with coronal radio emission (an 18\% system detection rate) and more than 600 background (most likely extra-galactic) sources. Among the targeted stars, we find a significant decline of the detection rate with age from 56$\pm$20\% for stars with ages $\le10$\,Myr to 10$\pm$3\% for stars with ages 100\,--\,200\,Myr. No star older than 200\,Myr was detected. The detection rate also declines with $T_{\rm eff}$ from 36$\pm$10\% for stars with $T_{\rm eff}<4000$\,K to 13$\pm$3\% for earlier spectral types with $T_{\rm eff}>5000$\,K. The binarity fraction among the radio-bright stars is at least twice as high as among the radio-quiet stars. The radio-bright nearby young stars identified here provide an interesting sample for future astrometric studies using VLBI arrays aimed at searching for hitherto unknown tight binary components or even exoplanets., Comment: 24 pages, 15 figures plus electronic figures with 31 figures, 3 tables, accepted by ApJ

Abridged: Direct imaging has made significant progress over the past decade leading to the detection of several giant planets. Observing strategies and data rates vary from instrument to instrument and wavelength, and can result in tens of thousands of images to be combined. We here present a new approach, tailored for VLT/NaCo observations performed with the Annular Groove Phase Mask (AGPM) coronagraph at $L'$ filter. Our pipeline aims at improving the post-processing of the observations on two fronts: identifying the location of the star behind the AGPM to better align the science frames and performing frame selection. Our method relies on finding the position of the AGPM in the sky frame observations, and correlate it with the circular aperture of the coronagraphic mask. This relationship allows us to retrieve the location of the AGPM in the science frames, in turn allowing us to estimate the position of the star. In the process we also gather additional information useful for our frame selection approach. We tested our pipeline on several targets, and find that we improve the S/N of companions around $\beta$ Pictoris and R CrA by $24\pm3$ \% and $117\pm11$ \% respectively, compared to other state-of-the-art reductions. The astrometry of the point sources is slightly different but remains compatible within $3\sigma$ compared to published values. Finally, we find that even for NaCo observations with tens of thousands of frames, frame selection yields just marginal improvement for point sources but may improve the final images for objects with extended emission such as disks. We proposed a novel approach to identify the location of the star behind a coronagraph even when it cannot easily be determined by other methods, leading to better S/N for nearby point sources, and led a thorough study on the importance of frame selection, concluding that the improvements are marginal in most case., Comment: Accepted for publication in A&A, November 2021

To understand how the multitude of planetary systems that have been discovered come to be, we need to study systems at different evolutionary stages, with different central stars but also in different environments. The most challenging environment for planet formation may be the harsh UV radiation field of nearby massive stars which quickly erodes disks by external photo-evaporation. We have observed the AT Pyx system, located in the head of a cometary globule in the Gum Nebula, to search for signs of ongoing planet formation. We used the extreme adaptive optics imager VLT/SPHERE to observe AT Pyx in polarized light as well as total intensity in the J, H and K-band. Additionally we employed VLT/NACO to observe the system in the L-band. We resolve the disk around AT Pyx in scattered light across multiple wavelengths. We find an extended (>126 au) disk, with an intermediate inclination between 35 deg and 42 deg. The disk shows complex sub-structure and we identify 2 and possibly 3 spiral-like features. Depending on the precise geometry of the disk (which we can not unambiguously infer from our data) the disk may be eccentric with an eccentricity of ~0.16 or partially self-shadowed. The spiral features and possible eccentricity are both consistent with signatures of an embedded gas giant planet equal in mass to Jupiter. Our own observations can rule out brown dwarf companions embedded in the resolved disk, but are not sensitive enough to detect gas giants. AT Pyx is the first disk in a cometray globule in the Gum Nebula which is spatially resolved. By comparison with disks in the Orion Nebula Cluster we note that the extension of the disk may be exceptional for this environment if the external UV radiation field is comparable to other cometary globules in the region. The signposts of ongoing planet formation are intriguing and need to be followed up with higher sensitivity., Comment: 11 pages, 9 figures, accepted for publication in A&A

Variable red- and blue-shifted absorption features observed in the Ca ii K line towards the A-type shell star $\phi$ Leo have been suggested by us in a previous work to be likely due to solid, comet-like bodies in the circumstellar (CS) environment. Our aim is to expand our observational study of this object to other characteristic spectral lines of A-type photospheres as well as to lines arising in their CS shells. We have obtained more than 500 high-resolution optical spectra collected at different telescopes from December 2015 to January 2019. We have analysed some photospheric lines, in particular Ca i 4226 \AA ~and Mg ii 4481 \AA, as well as the circumstellar shell lines Ca ii H\&K, Ca ii IR triplet, Fe ii, Ti ii, and the Balmer lines H$\alpha$ and H$\beta$. Our observational study reveals that $\phi$ Leo is a variable $\delta$ Scuti star whose spectra show remarkable dumps and bumps superimposed on the photospheric line profiles, which vary their strength and sharpness, propagate from blue- to more red-shifted radial velocities and persisting during a few hours, likely produced by non-radial pulsations. At the same time, all shell lines present an emission at $\sim$3 km/s centered at the core of the CS features, and two variable absorption minima at both sides of the emission. The variations observed in the Ca ii H\&K, Fe ii and Ti ii lines occur at any time scale from minutes to days and observing run, but without any clear correlation or recognizable temporal pattern among the different lines. In the case of H$\alpha$ the CS contribution is also variable in just one of the observing runs. We suggest that $\phi$ Leo is a rapidly rotating $\delta$ Scuti star surrounded by a variable, (nearly) edge-on CS disk possibly re-supplied by the $\delta$ Scuti pulsations., Comment: Accepted in Astronomy&Astrophysics. 15 pages, 15 figures. C1 table available on CDS

Recent observations of resolved cold debris disks at tens of au have revealed that gaps could be a common feature in these Kuiper belt analogues. Such gaps could be evidence for the presence of planets within the gaps or closer-in near the edges of the disk. We present SPHERE observations of HD 92945 and HD 107146, two systems with detected gaps. We constrained the mass of possible companions responsible for the gap to 1-2 M Jup for planets located inside the gap and to less than 5 M Jup for separations down to 20 au from the host star. These limits allow us to exclude some of the possible configurations of the planetary systems proposed to explain the shape of the disks around these two stars. In order to put tighter limits on the mass at very short separations from the star, where direct imaging data are less effective, we also combined our data with astrometric measurements from Hipparcos and Gaia and radial velocity measurements. We were able to limit the separation and the mass of the companion potentially responsible for the proper motion anomaly of HD 107146 to values of 2-7 au and 2-5 M Jup , respectively., Comment: 17 pages, 14 Figures, accepted for publication on MNRAS

While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events interpreted as exocomets (Falling Evaporating Bodies) around $\beta$ Pic in the early 80s, only $\sim$20 stars have been reported to host exocomet-like events. We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity. We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data have been collected in 14 observing campaigns expanding over 2 years from both hemispheres. We have analysed the Ca ii K&H and Na i D lines in order to search for non-photospheric absorptions originated in the circumstellar environment, and for variable events that could be caused by outgassing of exocomet-like bodies. We have detected non-photospheric absorptions towards 50% of the sample, attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas is detected in the metallic lines inspected via narrow stable absorptions, and/or variable blue-/red-shifted absorption events. Such variable events were found in 18 stars in the Ca ii and/or Na i lines; 6 of them are reported in the context of this work for the first time. In some cases the variations we report in the Ca ii K line are similar to those observed in $\beta$ Pic. While we do not find a significant trend with the age or location of the stars, we do find that the probability of finding CS gas in stars with larger vsin i is higher. We also find a weak trend with the presence of near-infrared excess, and with anomalous ($\lambda$ Boo-like) abundances, but this would require confirmation by expanding the sample., Comment: Accepted in A&A on March 23rd 2020

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. The achievements obtained thus far with SPHERE (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. The SPHERE+ project capitalizes on the expertise and lessons learned from SPHERE to push high contrast imaging performance to its limits on the VLT 8m-telescope. The scientific program of SPHERE+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and WFIRST). While SPHERE has sampled the outer parts of planetary systems beyond a few tens of AU, SPHERE+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. Building on SPHERE's scientific heritage and resounding success, SPHERE+ will be a dedicated survey instrument which will strengthen the leadership of ESO and the European community in the very competitive field of direct imaging of exoplanetary systems. With enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei., Comment: White paper submitted to ESO on Feb. 20th, 2020

The occurrence rate of long-period giant planets around young stars is highly uncertain since it is not only governed by the protoplanetary disc structure and planet formation process, but also reflects dynamical re-structuring processes after planet formation as well as possible capture of planets not formed in-situ. Direct imaging is currently the only feasible method to detect such wide-orbit planets and constrain their occurrence rate. We carry out a large L'-band high-contrast direct imaging survey for giant planets around young stars with protoplanetary or debris discs using the NACO instrument at the ESO Very Large Telescope on Cerro Paranal in Chile. We use very deep angular differential imaging observations with typically >60 deg field rotation, and employ a vector vortex coronagraph where feasible to achieve the best possible point source sensitivity down to an inner working angle of about 100mas. This paper introduces our NACO Imaging Survey for Planets around Young stars ("NACO-ISPY"), its goals and strategy, the target list, and data reduction scheme, and presents preliminary results from the first 2.5 survey years. We achieve a mean 5 sigma L' contrast of 6.4mag at 150mas and a background limit of 16.5mag at >1.5". Our detection probability is >50\% for companions with 8\,M$_{\rm Jup}$\ at semi-major axes 80-200au. It thus compares well to the detection space of other state-of-the-art high-contrast imaging surveys. We have contributed to the characterisation of two new planets originally discovered by VLT/SPHERE, but we have not yet independently discovered new planets around any of our target stars. We report the discovery of close-in low-mass stellar companions around four young stars and show L'-band scattered light images of the discs around eleven stars, six of which have never been imaged at L'-band before., Comment: 25 pages, 14 figures

Statistical analyses from exoplanet surveys around low-mass stars indicate that super-Earth and Neptune-mass planets are more frequent than gas giants around such stars, in agreement with core accretion theory of planet formation. Using precise radial velocities derived from visual and near-infrared spectra, we report the discovery of a giant planet with a minimum mass of 0.46 Jupiter masses in an eccentric 204-day orbit around the very low-mass star GJ 3512. Dynamical models show that the high eccentricity of the orbit is most likely explained from planet-planet interactions. The reported planetary system challenges current formation theories and puts stringent constraints on the accretion and migration rates of planet formation and evolution models, indicating that disc instability may be more efficient in forming planets than previously thought., Comment: Manuscript author version. 41 pages, 11 figures

Context. Teegarden's Star is the brightest and one of the nearest ultra-cool dwarfs in the solar neighbourhood. For its late spectral type (M7.0V), the star shows relatively little activity and is a prime target for near-infrared radial velocity surveys such as CARMENES. Aims. As part of the CARMENES search for exoplanets around M dwarfs, we obtained more than 200 radial-velocity measurements of Teegarden's Star and analysed them for planetary signals. Methods. We find periodic variability in the radial velocities of Teegarden's Star. We also studied photometric measurements to rule out stellar brightness variations mimicking planetary signals. Results. We find evidence for two planet candidates, each with $1.1M_\oplus$ minimum mass, orbiting at periods of 4.91 and 11.4 d, respectively. No evidence for planetary transits could be found in archival and follow-up photometry. Small photometric variability is suggestive of slow rotation and old age. Conclusions. The two planets are among the lowest-mass planets discovered so far, and they are the first Earth-mass planets around an ultra-cool dwarf for which the masses have been determined using radial velocities., Comment: A&A 627, A49. 26 pages, 17 figures, 6 tables. Press release available at http://www.astro.physik.uni-goettingen.de/~zechmeister/teegarden/teegarden.html. v2: two authors and one reference added

Within the NaCo-ISPY exoplanet imaging program, we aim at detecting and characterizing the population of low-mass companions at wide separations ($\gtrsim$10AU), focusing in particular on young stars either hosting a known protoplanetary disk or a debris disk. R CrA is one of the youngest (1-3 Myr) and most promising objects in our sample because of two previous studies that suggested the presence of a close companion. Our aim is to directly image and characterize the companion for the first time. We observed R CrA twice with the NaCo instrument at VLT in the $L'$ filter with a one year time baseline in between. The high-contrast imaging data were reduced and analyzed, and in both datasets the companion candidate was detected. The companion is detected at a separation of $196.8\pm4.5$/$196.6\pm5.9$ mas ($18.7\pm1.3$/$18.7\pm1.4$ AU) and position angle of $134.7\pm0.5^\circ/133.7\pm0.7^\circ$ in the first/second epoch observation. We measure a contrast of $7.29\pm0.18$/$6.70\pm0.15$ mag with respect to the primary. Stellar proper motion study rejects the hypothesis of the signal being a background object. The companion candidate orbits in the clockwise direction and, if on a face-on circular orbit, its period is $\sim43-47$ yr. This value disagrees with the estimated orbital motion and therefore a face-on circular orbit may be excluded. Depending on the assumed age, extinction and brightness of the primary, the stellar companion has a mass between $0.10\pm0.02\, M_\odot$ and $1.03^{+0.20}_{-0.18}\,M_\odot$ range, if no contribution from circumsecondary material is taken into account. The presence of the companion needs to be taken into account when analyzing the complex circumstellar environment of R CrA., Comment: Accepted for publication in A&A (7 pages, 3 figures, 3 tables)

HIP 65426 b is a recently discovered exoplanet imaged during the course of the SPHERE-SHINE survey. Here we present new $L'$ and $M'$ observations of the planet from the NACO instrument at the VLT from the NACO-ISPY survey, as well as a new $Y-H$ spectrum and $K$-band photometry from SPHERE-SHINE. Using these data, we confirm the nature of the companion as a warm, dusty planet with a mid-L spectral type. From comparison of its SED with the BT-Settl atmospheric models, we derive a best-fit effective temperature of $T_{\text{eff}}=1618\pm7$ K, surface gravity $\log g=3.78^{+0.04}_{-0.03}$ and radius $R=1.17\pm0.04$ $R_{\text{J}}$ (statistical uncertainties only). Using the DUSTY and COND isochrones we estimate a mass of $8\pm1$ $M_{\text{J}}$. Combining the astrometric measurements from our new datasets and from the literature, we show the first indications of orbital motion of the companion (2.6$\sigma$ significance) and derive preliminary orbital constraints. We find a highly inclined orbit ($i=107^{+13}_{-10}$ deg) with an orbital period of $800^{+1200}_{-400}$ yr. We also report SPHERE sparse aperture masking observations that investigate the possibility that HIP 65426 b was scattered onto its current orbit by an additional companion at a smaller orbital separation. From this data we rule out the presence of brown dwarf companions with masses greater than 16 $M_{\text{J}}$ at separations larger than 3 AU, significantly narrowing the parameter space for such a companion., Comment: Accepted for publication in A&A

Young circumstellar disks are of prime interest to understand the physical and chemical conditions under which planet formation takes place. Only very few detections of planet candidates within these disks exist, and most of them are currently suspected to be disk features. In this context, the transition disk around the young star PDS 70 is of particular interest, due to its large gap identified in previous observations, indicative of ongoing planet formation. We aim to search for the presence of planets and search for disk structures indicative for disk-planet interactions and other evolutionary processes. We analyse new and archival near-infrared (NIR) images of the transition disk PDS 70 obtained with the VLT/SPHERE, VLT/NaCo and Gemini/NICI instruments in polarimetric differential imaging (PDI) and angular differential imaging (ADI) modes. We detect a point source within the gap of the disk at about 195 mas (about 22 au) projected separation. The detection is confirmed at five different epochs, in three filter bands and using different instruments. The astrometry results in an object of bound nature, with high significance. The comparison of the measured magnitudes and colours to evolutionary tracks suggests that the detection is a companion of planetary mass. We confirm the detection of a large gap of about 54 au in size within the disk in our scattered light images, and detect a signal from an inner disk component. We find that its spatial extent is very likely smaller than about 17 au in radius. The images of the outer disk show evidence of a complex azimuthal brightness distribution which may in part be explained by Rayleigh scattering from very small grains. Future observations of this system at different wavelengths and continuing astrometry will allow us to test theoretical predictions regarding planet-disk interactions, planetary atmospheres and evolutionary models., Comment: 23 pages, accepted by A&A

We report on the first star discovered to host a planet detected by radial velocity (RV) observations obtained within the CARMENES survey for exoplanets around M dwarfs. HD 147379 ($V = 8.9$ mag, $M = 0.58 \pm 0.08$ M$_{\odot}$), a bright M0.0V star at a distance of 10.7 pc, is found to undergo periodic RV variations with a semi-amplitude of $K = 5.1\pm0.4$ m s$^{-1}$ and a period of $P = 86.54\pm0.06$ d. The RV signal is found in our CARMENES data, which were taken between 2016 and 2017, and is supported by HIRES/Keck observations that were obtained since 2000. The RV variations are interpreted as resulting from a planet of minimum mass $m_{\rm p}\sin{i} = 25 \pm 2$ M$_{\oplus}$, 1.5 times the mass of Neptune, with an orbital semi-major axis $a = 0.32$ au and low eccentricity ($e < 0.13$). HD 147379b is orbiting inside the temperate zone around the star, where water could exist in liquid form. The RV time-series and various spectroscopic indicators show additional hints of variations at an approximate period of 21.1d (and its first harmonic), which we attribute to the rotation period of the star., Comment: accepted for publication as A&A Letter

The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520--1710nm at a resolution of at least $R > 80,000$, and we measure its RV, H$\alpha$ emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, $Q$, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700--900nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1ms$^{-1}$ in very low mass M dwarfs at longer wavelengths likely requires the use of a 10m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3-4ms$^{-1}$., Comment: accepted for publication in A&A, 13 pages plus 40 pages spectral atlas, first 10 atlas pages are reduced in quality to fit arXiv size limit; one CARMENES spectrum for each of the 324 stars is published in electronic format at http://carmenes.cab.inta-csic.es/

Context: The CARMENES survey is a high-precision radial velocity (RV) programme that aims to detect Earth-like planets orbiting low-mass stars. Aims: We develop least-squares fitting algorithms to derive the RVs and additional spectral diagnostics implemented in the SpEctrum Radial Velocity Analyser (SERVAL), a publicly available python code. Methods: We measured the RVs using high signal-to-noise templates created by coadding all available spectra of each star.We define the chromatic index as the RV gradient as a function of wavelength with the RVs measured in the echelle orders. Additionally, we computed the differential line width by correlating the fit residuals with the second derivative of the template to track variations in the stellar line width. Results: Using HARPS data, our SERVAL code achieves a RV precision at the level of 1m/s. Applying the chromatic index to CARMENES data of the active star YZ CMi, we identify apparent RV variations induced by stellar activity. The differential line width is found to be an alternative indicator to the commonly used full width half maximum. Conclusions: We find that at the red optical wavelengths (700--900 nm) obtained by the visual channel of CARMENES, the chromatic index is an excellent tool to investigate stellar active regions and to identify and perhaps even correct for activity-induced RV variations., Comment: 13 pages, 13 figures. A&A in press. Code is available at https://github.com/mzechmeister/serval

Context: The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M-dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ15A, GJ176, GJ436, GJ536 and GJ1148) or are multiple planetary systems (GJ581 and GJ876). Aims: We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES. Methods: We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems are fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability. Results: We confirm or provide supportive arguments for planets around all the investigated stars except for GJ15A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ15Ab, we show evidence for a possible long-period ($P_{\rm c}$ = 7025$_{-629}^{+972}$ d) Saturn-mass ($m_{\rm c} \sin i$ = 51.8$_{-5.8}^{+5.5}M_\oplus$) planet around GJ15A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ1148, for which we estimate a period $P_{\rm c}$ = 532.6$_{-2.5}^{+4.1}$ d, eccentricity $e_{\rm c}$ = 0.34$_{-0.06}^{+0.05}$ and minimum mass $m_{\rm c} \sin i$ = 68.1$_{-2.2}^{+4.9}M_\oplus$. Conclusions: The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars., Comment: Accepted for publication in A&A, 24 pages, 16 figures, 14 tables

Density profiles of isolated cores derived from thermal dust continuum emission rely on models of dust properties, such as mass opacity, which are poorly constrained. With complementary measures from near-infrared extinction maps, we can assess the reliability of commonly-used dust models. In this work, we compare Herschel-derived maps of the optical depth with equivalent maps derived from CFHT WIRCAM near-infrared observations for three isolated cores: CB68, L429, and L1552. We assess the dust opacities provided from four models: OH1a, OH5a, Orm1, and Orm4. Although the consistency of the models differs between the three sources, the results suggest that the optical properties of dust in the envelopes of the cores are best described by either silicate and bare graphite grains (e.g., Orm1) or carbonaceous grains with some coagulation and either thin or no ice mantles (e.g., OH5a). None of the models, however, individually produced the most consistent optical depth maps for every source. The results suggest that either the dust in the cores is not well described by any one dust property model, the application of the dust models cannot be extended beyond the very center of the cores, or more complex SED fitting functions are necessary., Comment: Accepted to ApJ, September 27, 2017

We present an intensive monitoring of high-resolution spectra of the Ca {\sc ii} K line in the A7IV shell star $\Phi$ Leo at very short (minutes, hours), short (night to night), and medium (weeks, months) timescales. The spectra show remarkable variable absorptions on timescales of hours, days, and months. The characteristics of these sporadic events are very similar to most that are observed toward the debris disk host star $\beta$ Pic, which are commonly interpreted as signs of the evaporation of solid, comet-like bodies grazing or falling onto the star. Therefore, our results suggest the presence of solid bodies around $\Phi$ Leo. To our knowledge, with the exception of $\beta$ Pic, our monitoring has the best time resolution at the mentioned timescales for a star with events attributed to exocomets. Assuming the cometary scenario and considering the timescales of our monitoring, our results indicate that $\Phi$ Leo presents the richest environment with comet-like events known to date, second only to $\beta$ Pic., Comment: A&A letters, proof-corrected

Constraining the temperature and density structure of dense molecular cloud cores is fundamental for understanding the initial conditions of star formation. We use Herschel observations of the thermal FIR dust emission from nearby isolated molecular cloud cores and combine them with ground-based submillimeter continuum data to derive observational constraints on their temperature and density structure. The aim of this study is to verify the validity of a ray-tracing inversion technique developed to derive the dust temperature and density structure of isolated starless cores directly from the dust emission maps and to test if the resulting temperature and density profiles are consistent with physical models. Using this ray-tracing inversion technique, we derive the dust temperature and density structure of six isolated starless cloud cores. We employ self-consistent radiative transfer modeling to the derived density profiles, treating the ISRF as the only heating source. The best-fit values of local strength of the ISRF and the extinction by the outer envelope are derived by comparing the self-consistently calculated temperature profiles with those derived by the ray-tracing method. We find that all starless cores are significantly colder inside than outside, with the core temperatures showing a strong negative correlation with peak column density. This suggests that their thermal structure is dominated by external heating from the ISRF and shielding by dusty envelopes. The temperature profiles derived with the ray-tracing inversion method can be well-reproduced with self-consistent radiative transfer models., Comment: 16 pages, 12 figures, accepted for publication in A&A

Given that a majority of stars form in multiple systems, in order to fully understand the star- and planet-formation processes we must seek to understand them in multiple stellar systems. With this in mind, we present an analysis of the enigmatic binary T-Tauri system VV Corona Australis, in which both components host discs, but only one is visible at optical wavelengths. We seek to understand the peculiarities of this system by searching for a model for the binary which explains all the available continuum observations of the system. We present new mid-infrared interferometry and near-infrared spectroscopy along with archival millimetre-wave observations, which resolve the binary at 1.3mm for the first time. We compute a grid of pre-main-sequence radiative transfer models and calculate their posterior probabilities given the observed spectral energy distributions and mid-infrared interferometric visibilities of the binary components, beginning with the assumption that the only differences between the two components are their inclination and position angles. Our best-fitting solution corresponds to a relatively low luminosity T-tauri binary, with each component's disc having a large scale height and viewed at moderate inclination ($\sim 50^\circ$), with the infrared companion inclined by $\sim 5^\circ$ degrees more than the primary. Comparing the results of our model to evolutionary models suggests stellar masses $\sim 1.7$M$_\odot$ and an age for the system of 3.5Myr, towards the upper end of previous estimates. Combining these results with accretion indicators from near-IR spectroscopy, we determine an accretion rate of 4.0$\times 10^{-8}$M$_\odot$ yr$^{-1}$ for the primary. We suggest that future observations of VV~CrA and similar systems should prioritise high angular resolution sub-mm and near-IR imaging of the discs and high resolution optical/NIR spectroscopy of the central stars., Comment: 17 pages, 11 figures, 4 tables. Recommended for acceptance to MNRAS

Context: The initial conditions for the gravitational collapse of molecular cloud cores and the subsequent birth of stars are still not well constrained. The characteristic cold temperatures (about 10 K) in such regions require observations at sub-millimetre and longer wavelengths. The Herschel Space Observatory and complementary ground-based observations presented in this paper have the unprecedented potential to reveal the structure and kinematics of a prototypical core region at the onset of stellar birth. Aims: This paper aims to determine the density, temperature, and velocity structure of the star-forming Bok globule CB 17. This isolated region is known to host (at least) two sources at different evolutionary stages: a dense core, SMM1, and a Class I protostar, IRS. Methods: We modeled the cold dust emission maps from 100 micron to 1.2 mm with both a modified blackbody technique to determine the optical depth-weighted line-of-sight temperature and column density and a ray-tracing technique to determine the core temperature and volume density structure. Furthermore, we analysed the kinematics of CB17 using the high-density gas tracer N2H+. Results: From the ray-tracing analysis, we find a temperature in the centre of SMM1 of 10.6 K, a flat density profile with radius 9500 au, and a central volume density of n(H) = 2.3x10^5 cm-3. The velocity structure of the N2H+ observations reveal global rotation with a velocity gradient of 4.3 km/s/pc. Superposed on this rotation signature we find a more complex velocity field, which may be indicative of differential motions within the dense core. Conclusions: SMM is a core in an early evolutionary stage at the verge of being bound, but the question of whether it is a starless or a protostellar core remains unanswered., Comment: published in A&A

In the summer of 2011, the first on-sky astrometric commissioning of PRIMA-Astrometry delivered a performance of 3 m'' for a 10 '' separation on bright objects, orders of magnitude away from its exoplanet requirement of 50 {\mu}'' ~ 20 {\mu}'' on objects as faint as 11 mag ~ 13 mag in K band. This contribution focuses on upgrades and characterizations carried out since then. The astrometric metrology was extended from the Coud\'e focus of the Auxillary Telescopes to their secondary mirror, in order to reduce the baseline instabilities and improve the astrometric performance. While carrying out this extension, it was realized that the polarization retardance of the star separator derotator had a major impact on both the astrometric metrology and the fringe sensors. A local compensation of this retardance and the operation on a symmetric baseline allowed a new astrometric commissioning. In October 2013, an improved astrometric performance of 160 {\mu}'' was demonstrated, still short of the requirements. Instabilities in the astrometric baseline still appear to be the dominating factor. In preparation to a review held in January 2014, a plan was developed to further improve the astrometric and faint target performance of PRIMA Astrometry. On the astrometric aspect, it involved the extension of the internal longitudinal metrology to primary space, the design and implementation of an external baseline metrology, and the development of an astrometric internal fringes mode. On the faint target aspect, investigations of the performance of the fringe sensor units and the development of an AO system (NAOMI) were in the plan. Following this review, ESO decided to take a proposal to the April 2014 STC that PRIMA be cancelled, and that ESO resources be concentrated on ensuring that Gravity and Matisse are a success. This proposal was recommended by the STC in May 2014, and endorsed by ESO., Comment: 12 pages, 9 figures, 2 tables, Proceeding of SPIE conference in Montreal

Young, nearby stars are ideal targets to search for planets using the direct imaging technique. The determination of stellar parameters is crucial for the interpretation of imaging survey results particularly since the luminosity of substellar objects has a strong dependence on system age. We have conducted a large program with NaCo at the VLT in order to search for planets and brown dwarfs in wide orbits around 86 stars. A large fraction of the targets observed with NaCo were poorly investigated in the literature. We performed a study to characterize the fundamental properties (age, distance, mass) of the stars in our sample. To improve target age determinations, we compiled and analyzed a complete set of age diagnostics. We measured spectroscopic parameters and age diagnostics using dedicated observations acquired with FEROS and CORALIE spectrographs at La Silla Observatory. We also made extensive use of archival spectroscopic data and results available in the literature. Additionally, we exploited photometric time-series, available in ASAS and Super-WASP archives, to derive rotation period for a large fraction of our program stars. We provided updated characterization of all the targets observed in the VLT NaCo Large program, a survey designed to probe the occurrence of exoplanets and brown dwarfs in wide orbits. The median distance and age of our program stars are 64 pc and 100 Myr, respectively. Nearly all the stars have masses between 0.70 and 1.50sun, with a median value of 1.01 Msun. The typical metallicity is close to solar, with a dispersion that is smaller than that of samples usually observed in radial velocity surveys. Several stars are confirmed or proposed here to be members of nearby young moving groups. Eight spectroscopic binaries are identified., Comment: 64 pages with Appendix, 15 figures, accepted to A&A

EX Lup-type objects (EXors) are low-mass pre-main sequence objects characterized by outbursts attributed to highly enhanced disk accretion. The trigger mechanism of EXor outbursts is still debated. One theory requires a close (sub)stellar companion that perturbs the inner disk and triggers the onset of the outburst. Here, we study the radial velocity (RV) variations of EX Lup, the prototype of EXors. We conducted a 5-year RV survey with HARPS and FEROS. We analyzed the activity of EX Lup by checking the bisector and several other activity indicators. We complemented the RV data with photometric monitoring to look for signatures of activity or varying accretion. We found that the RV of EX Lup is periodic, with stable period, semi-amplitude, and phase over at least four years of observations. This period is not present in any of the activity indicators. However, the RV of narrow metallic emission lines suggest the same period, but with an anti-correlating phase. The observed absorption line RVs can be fitted with a Keplerian solution around a 0.6 M_Sun central star with M2 sin i = (14.7 +/- 0.7) M_Jup and eccentricity of e = 0.24. Alternatively, we attempted to model the observations with a cold/hot stellar spot as well, but the spot parameters needed to reproduce the RV semi-amplitude are in contradiction with the photometric variability, making the spot scenario unlikely. We discuss two possibilities to explain the RV data: a geometry with two accretion columns rotating with the star, and a single accretion flow synchronized with the orbital motion of the hypothetical companion. In the companion scenario, the companion's mass would fall into the brown dwarf desert, which, together with the unusually small separation would make EX Lup a unique binary system, with interesting implications on the physical mechanisms responsible for triggering the outburst., Comment: 10 pages, 9 figures, 3 tables, accepted for publication in A&A

Seven isolated, nearby low-mass starless molecular cloud cores have been observed as part of the Herschel key program Earliest Phases of Star formation (EPoS). By applying a ray-tracing technique to the obtained continuum emission and complementary (sub)mm emission maps, we derive the physical structure (density, dust temperature) of these cloud cores. We present observations of the 12CO, 13CO, and C18O (2-1) and N2H+ (1-0) transitions towards the same cores. Based on the density and temperature profiles, we apply time-dependent chemical and line-radiative transfer modeling and compare the modeled to the observed molecular emission profiles. CO is frozen onto the grains in the center of all cores in our sample. The level of CO depletion increases with hydrogen density and ranges from 46% up to more than 95% in the core centers in the core centers in the three cores with the highest hydrogen density. The average hydrogen density at which 50% of CO is frozen onto the grains is 1.1+-0.4 10^5 cm^-3. At about this density, the cores typically have the highest relative abundance of N2H+. The cores with higher central densities show depletion of N2H+ at levels of 13% to 55%. The chemical ages for the individual species are on average 2+-1 10^5 yr for 13CO, 6+-3 10^4 yr for C18O, and 9+-2 10^4 yr for N2H+. Chemical modeling indirectly suggests that the gas and dust temperatures decouple in the envelopes and that the dust grains are not yet significantly coagulated. We observationally confirm chemical models of CO-freezeout and nitrogen chemistry. We find clear correlations between the hydrogen density and CO depletion and the emergence of N2H+. The chemical ages indicate a core lifetime of less than 1 Myr., Comment: 24 pages, 25 figures, Accepted for publication in Astronomy and Astrophysics

Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. The DUNES survey aims at detecting extra-solar analogues to the Edgeworth-Kuiper belt around solar-type stars, putting in this way the solar system into context. The survey allows us to address some questions related to the prevalence and properties of planetesimal systems. We used {\it Herschel}/PACS to observe a sample of nearby FGK stars. Data at 100 and 160 $\mu$m were obtained, complemented in some cases with observations at 70 $\mu$m, and at 250, 350 and 500 $\mu$m using SPIRE. The observing strategy was to integrate as deep as possible at 100 $\mu$m to detect the stellar photosphere. Debris discs have been detected at a fractional luminosity level down to several times that of the Edgeworth-Kuiper belt. The incidence rate of discs around the DUNES stars is increased from a rate of $\sim$ 12.1% $\pm$ 5% before \emph{Herschel} to $\sim$ 20.2% $\pm$ 2%. A significant fraction ($\sim$ 52%) of the discs are resolved, which represents an enormous step ahead from the previously known resolved discs. Some stars are associated with faint far-IR excesses attributed to a new class of cold discs. Although it cannot be excluded that these excesses are produced by coincidental alignment of background galaxies, statistical arguments suggest that at least some of them are true debris discs. Some discs display peculiar SEDs with spectral indexes in the 70-160$\mu$m range steeper than the Rayleigh-Jeans one. An analysis of the debris disc parameters suggests that a decrease might exist of the mean black body radius from the F-type to the K-type stars. In addition, a weak trend is suggested for a correlation of disc sizes and an anticorrelation of disc temperatures with the stellar age.

Aims: We study the fragmentation and dynamical properties of a massive starless gas clump at the onset of high-mass star formation. Methods: Based on Herschel continuum data we identify a massive gas clump that remains far-infrared dark up to 100mum wavelengths. The fragmentation and dynamical properties are investigated by means of Plateau de Bure Interferometer and Nobeyama 45m single-dish spectral line and continuum observations. Results: The massive gas reservoir fragments at spatial scales of ~18000AU in four cores. Comparing the spatial extent of this high-mass region with intermediate- to low-mass starless cores from the literature, we find that linear sizes do not vary significantly over the whole mass regime. However, the high-mass regions squeeze much more gas into these similar volumes and hence have orders of magnitude larger densities. The fragmentation properties of the presented low-to high-mass regions are consistent with gravitational instable Jeans fragmentation. Furthermore, we find multiple velocity components associated with the resolved cores. Recent radiative transfer hydrodynamic simulations of the dynamic collapse of massive gas clumps also result in multiple velocity components along the line of sight because of the clumpy structure of the regions. This result is supported by a ratio between viral and total gas mass for the whole region <1. Conclusions: This apparently still starless high-mass gas clump exhibits clear signatures of early fragmentation and dynamic collapse prior to the formation of an embedded heating source. A comparison with regions of lower mass reveals that the linear size of star-forming regions does not necessarily have to vary much for different masses, however, the mass reservoirs and gas densities are orders of magnitude enhanced for high-mass regions compared to their lower-mass siblings., Comment: 11 pages, 10 figures, accepted to Astronomy and Astrophysics, high-resolution version with all figures included can be found at http://www.mpia.de/homes/beuther/papers.html

We present a possible identification strategy for first hydrostatic core (FHSC) candidates and make predictions of ALMA dust continuum emission maps from these objects. We analyze the results given by the different bands and array configurations and identify which combinations of the two represent our best chance of solving the fragmentation issue in these objects. If the magnetic field is playing a role, the emission pattern will show evidence of a pseudo-disk and even of a magnetically driven outflow, which pure hydrodynamical calculations cannot reproduce., Comment: 2 pages, to appear in the proceedings of the conference "New Trends in Radio Astronomy in the ALMA Era", Hakone, Japan, December 3-8, 2012

Observations of the circumstellar disk in the Bok globule CB 26 at 110, 230, and 270 GHz are presented together with the results of the simulations and estimates of the disk parameters. These observations were obtained using the SMA, IRAM Plateau de Bure, and OVRO interferometers. The maps have relatively high angular resolutions (0.4-1"), making it possible to study the spatial structure of the gas-dust disk. The disk parameters are reconstructed via a quantitative comparison of observational and theoretical intensity maps. The disk model used to construct the theoretical maps is based on the assumption of hydrostatic and radiative equilibrium in the vertical direction, while the radial surface density profile is described phenomenologically. The system of equations for the transfer of the infrared and ultraviolet radiation is solved in the vertical direction, in order to compute the thermal structure of the disk. The disk best-fit parameters are derived for each map and all the maps simultaneously, using a conjugate gradient method. The degrees of degeneracy of the parameters describing the thermal structure and density distribution of the disk are analyzed in detail. All three maps indicate the presence of an inner dust-free region with a radius of approximately 35 AU, in agreement with the conclusions of other studies. The inclination of the disk is 78 deg, which is smaller than the value adopted in our earlier study of rotating molecular outflows from CB 26. The model does not provide any evidence for the growth of dust particles above a_max=0.02 cm., Comment: 15 pages, 9 figures, 2 tables

The temperature and density structure of molecular cloud cores are the most important physical quantities that determine the course of the protostellar collapse and the properties of the stars they form. Nevertheless, density profiles often rely either on the simplifying assumption of isothermality or on observationally poorly constrained model temperature profiles. With the aim of better constraining the initial physical conditions in molecular cloud cores at the onset of protostellar collapse, we initiated the Guaranteed Time Key Project (GTKP) "The Earliest Phases of Star Formation" (EPoS) with the Herschel satellite. This paper gives an overview of the low-mass sources in the EPoS project, including all observations, the analysis method, and the initial results of the survey. We study the thermal dust emission of 12 previously well-characterized, isolated, nearby globules using FIR and submm continuum maps at up to eight wavelengths between 100 micron and 1.2 mm. Our sample contains both globules with starless cores and embedded protostars at different early evolutionary stages. The dust emission maps are used to extract spatially resolved SEDs, which are then fit independently with modified blackbody curves to obtain line-of-sight-averaged dust temperature and column density maps. We find that the thermal structure of all globules is dominated by external heating from the interstellar radiation field and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (8-12 K). The protostars embedded in some of the globules raise the local temperature of the dense cores only within radii out to about 5000 AU, but do not significantly affect the overall thermal balance of the globules., Comment: 35 pages, 47 figures, Accepted for publication in Astronomy and Astrophysics

The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for the discovery and study of planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years and to detect their barycentric motions due to orbiting planets. We present the operation principle, the instrument's implementation, and the results of a first series of test observations. A comprehensive overview of the instrument infrastructure is given and the observation strategy for dual-field relative astrometry is presented. The differential delay lines, a key component of the PRIMA facility which was delivered by the ESPRI consortium, are described and their performance within the facility is discussed. Observations of bright visual binaries are used to test the observation procedures and to establish the instrument's astrometric precision and accuracy. The data reduction strategy for astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO are used as an independent verification of PRIMA astrometric observations. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 micro-arcseconds was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain which is not monitored by the internal metrology system. Our observations led to the definition of corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets., Comment: 32 pages, 39 figures, Accepted for publication in Astronomy and Astrophysics

(Abriged) In the framework of the Herschel GTKP "The earliest phases of star formation", we have imaged B68 between 100 and 500 um. Ancillary (sub)mm data, spectral line maps of the 12/13CO(2-1) transitions as well as a NIR extinction map were added to the analysis. We employed a ray-tracing algorithm to derive the 2D mid-plane dust temperature and volume density distribution without suffering from LoS averaging effects of simple SED fitting procedures. Additional 3D radiative transfer calculations were employed to investigate the connection between the external irradiation and the peculiar crescent shaped morphology found in the FIR maps. For the first time, we spatially resolve the dust temperature and density distribution of B68. We find T_dust dropping from 16.7 K at the edge to 8.2 K in the centre, which is about 4 K lower than the result of the simple SED fitting approach. N_H peaks at 4.3x10^22 cm^-2 and n_H at 3.4x10^5 cm^-3 in the centre. B68 has a mass of 3.1 M_sun of material with A_K > 0.2 mag for an assumed distance of 150 pc. We detect a compact source in the southeastern trunk, which is also seen in extinction and CO. We find the radial density distribution from the edge of the inner plateau outward to be n_H ~ r^-3.5. Such a steep profile can arise from either or both of the following: external irradiation with a significant UV contribution or the fragmentation of filamentary structures. Our 3D radiative transfer model of an externally irradiated core by an anisotropic ISRF reproduces the crescent morphology. Our CO observations show that B68 is part of a chain of globules in both space and velocity, which may indicate that it was once part of a filament which dispersed. We also resolve a new compact source in the SE trunk and find that it is slightly shifted in centroid velocity from B68, lending qualitative support to core collision scenarios., Comment: Accepted for publication by A&A, 21 pages (+ appendix), 21 figures

The Extrasolar Planet Search with PRIMA project (ESPRI) aims at characterising and detecting extrasolar planets by measuring the host star's reflex motion using the narrow-angle astrometry capability of the PRIMA facility at the Very Large Telescope Interferometer. A first functional demonstration of the astrometric mode was achieved in early 2011. This marked the start of the astrometric commissioning phase with the purpose of characterising the instrument's performance, which ultimately has to be sufficient for exoplanet detection. We show results obtained from the observation of bright visual binary stars, which serve as test objects to determine the instrument's astrometric precision, its accuracy, and the plate scale. Finally, we report on the current status of the ESPRI project, in view of starting its scientific programme., Comment: 11 pages, 6 figures. To appear in the proceedings of the 2012 SPIE Conference "Astronomical Telescopes and Instrumentation"

Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30m telescope by using the new broad band correlator (FTS) to search for so far undetected molecules in the protoplanetary disks surrounding the TTauri stars DM Tau, GO Tau, LkCa 15 and the Herbig Ae star MWC 480. We report the first detection of HC3N at 5 sigma in the GO Tau and MWC 480 disks with the IRAM 30-m, and in the LkCa 15 disk (5 sigma), using the IRAM array, with derived column densities of the order of 10^{12}cm^{-2}. We also obtain stringent upper limits on CCS (N < 1.5 x 10^{12} cm^{-3}). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen and sulfur-bearing molecule observations. The observed column densities of HC3N are typically two orders of magnitude lower than the existing predictions and appear to be lower in the presence of strong UV flux, suggesting that the molecular chemistry is sensitive to the UV penetration through the disk. The CCS upper limits reinforce our model with low elemental abundance of sulfur derived from other sulfur-bearing molecules (CS, H2S and SO)., Comment: 8 pages, 4 figures, 3 tables, Accepted for publication in ApJ

Context: The earliest stages of high-mass star formation are still poorly characterized. It is also unknown whether the initial conditions vary with environment. Aims: We want to investigate the youngest massive gas clumps in the environment of extremely active star formation. Methods: We selected the IRDC18454 complex associated with the W43 Galactic mini-starburst, and observed it in the continuum emission between 70mu and 1.2mm, and in spectral line emission of N2H+ and 13CO with single-dish instruments and an interferometer. Results: The multi-wavelength continuum study allows us to identify clumps that are infrared dark even at 70mu and hence the best candidates to be genuine high-mass starless gas clumps. The spectral energy distributions reveal elevated temperatures and luminosities compared to more quiescent environments. Furthermore, we identify a temperature gradient from the W43 mini-starburst toward the starless clumps. We discuss whether the radiation impact of the nearby mini-starburst changes the fragmentation properties of the gas clumps and by that maybe favors more high-mass star formation in such an environment. The spectral line data reveal two different velocity components of the gas at 100 and 50km/s. While chance projection is a possibility to explain these components, the projected associations of the emission sources as well as the prominent location at the Galactic bar -- spiral arm interface also allow the possibility that these two components may be spatially associated and even interacting. Conclusions: High-mass starless gas clumps can exist in the close environment of very active star formation without being destroyed. The impact of the active star formation sites may even allow for more high-mass stars to form in these 2nd generation gas clumps., Comment: 12 pages, 12 figures, accepted for A&A, high-resolution version at http://www.mpia-hd.mpg.de/homes/beuther/papers.html

We pursue the investigation of a previously proposed correlation between chemical properties and physical evolutionary stage of isolated low-mass star-forming regions. In the past, the NH3/CCS abundance ratio was suggested to be a potentially useful indicator for the evolutionary stage of cloud cores. We aim to study its applicability for isolated Bok globules. A sample of 42 Bok globules with and without signs of current star formation was searched for CCS(2-1) emission, the observations were complemented with NH3 measurements available in the literature and own observations. The abundance ratio of both molecules is discussed with respect to the evolutionary stage of the objects and in the context of chemical models. The NH3/CCS ratio could be assessed for 18 Bok globules and is found to be moderately high and roughly similar across all evolutionary stages from starless and prestellar cores towards internally heated cores harbouring protostars of Class 0, Class I or later. Bok globules with extremely high CCS abundance analogous to carbon-chain producing regions in dark cloud cores are not found. The observed range of NH3/CCS hints towards a relatively evolved chemical state of all observed Bok globules., Comment: 12 pages, 6 figures, accepted for publication in Astronomy & Astrophysics

We present new imaging and spectroscopic data of the young Herbig star HD 144432 A, which was known to be a binary star with a separation of 1.47 arcsec. High-resolution NIR imaging data obtained with NACO at the VLT reveal that HD 144432 B itself is a close binary pair with a separation of 0.1 arcsec. High-resolution optical spectra, acquired with FEROS at the 2.2m MPG/ESO telescope in La Silla, of the primary star and its co-moving companions were used to determine their main stellar parameters such as effective temperature, surface gravity, radial velocity, and projected rotational velocity by fitting synthetic spectra to the observed stellar spectra. The two companions, HD 144432 B and HD 144432 C, are identified as low-mass T Tauri stars of spectral type K7V and M1V, respectively. From the position in the HRD the triple system appears to be co-eval with a system age of 6+/-3 Myr., Comment: Accepted for publication in Astronomy & Astrophysics, 4 pages, 4 figures

HD 61005 is a nearby young solar type star that shows a large infrared excess due to a debris disk. The disk has been recently imaged from ground and space, with indications of several components. Some characteristics of the disk suggest the presence of planetary companions around the star, that remain undetected in deep adaptive optics imaging. For a better understanding of the system we aim to refine the determination of the stellar parameters, with emphasis on the stellar age and system orientation. We used ASAS and Hipparcos photometry and FEROS spectra to determine the rotation period, radial and rotational velocity, chromospheric emission, effective temperature, and chemical composition. We find no indication of any misalignment between the star rotation axis and the disk. The standard age calibrations applied to several indicators yield an age close to that of the Pleiades (120 Myr); however the kinematic properties strongly support its membership in the younger (40 Myr) Argus association, which also includes the IC 2391 open cluster. Detailed comparison of the properties of HD 61005 and IC 2391 members shows that the characteristics of HD 61005 are compatible with membership to the Argus association, once its rather slow rotation is taken into account, because lithium and other age indicators are somewhat correlated with stellar rotation at a fixed age. We also identify systematic differences between the field and cluster population of the Argus association, which are probably selection effects, so we suggest that additional members with slower rotation and lower activity level are waiting to be identified., Comment: A&A, in press, 13 pages, 11 figures

Abridged: We detail and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. We consider three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking is performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. Using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form, the chemical evolution is modeled within 10^9 years. The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result however required a lot of efforts to make all necessary details consistent through the model runs, e.g. definition of the gas particle density, density of grain surface sites, the strength and shape of the UV radiation field, etc. The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available in the Internet: http://www.mpia.de/homes/semenov/Chemistry_benchmark/home.html, Comment: 12 pages, 5 figures, 3 tables, accepted for publication in A&A. The relevant web page is: http://www.mpia.de/homes/semenov/Chemistry_benchmark/home.html

We present the first far-IR observations of the solar-type stars delta Pav, HR 8501, 51 Peg and zeta^2 Ret, taken within the context of the DUNES Herschel Open Time Key Programme (OTKP). This project uses the PACS and SPIRE instruments with the objective of studying infrared excesses due to exo-Kuiper belts around nearby solar-type stars. The observed 100 um fluxes from delta Pav, HR 8501, and 51 Peg agree with the predicted photospheric fluxes, excluding debris disks brighter than Ldust/Lstar ~ 5 x 10^-7 (1 sigma level) around those stars. A flattened, disk-like structure with a semi-major axis of ~ 100 AU in size is detected around zeta^2 Ret. The resolved structure suggests the presence of an eccentric dust ring, which we interpret as an exo-Kuiper belt with Ldust/Lstar ~ 10^-5., Comment: 5 pages, 2 figures

About two dozen exo-solar debris systems have been spatially resolved. These debris discs commonly display a variety of structural features such as clumps, rings, belts, eccentric distributions and spiral patterns. In most cases, these features are believed to be formed, shaped and maintained by the dynamical influence of planets orbiting the host stars. In very few cases has the presence of the dynamically important planet(s) been inferred from direct observation. The solar-type star q1 Eri is known to be surrounded by debris, extended on scales of < 30''. The star is known to host at least one planet, albeit on an orbit far too small to make it responsible for structures at distances of tens to hundreds of AU. The aim of the present investigation is twofold: to determine the optical and material properties of the debris and to infer the spatial distribution of the dust, which may hint at the presence of additional planets. The photodetector array camera and spectrometer (PACS) aboard the Herschel Space Observatory allows imaging observations in the far infrared at unprecedented resolution, i.e. at better than 6'' to 12'' over the wavelength range of 60 {\mu}m to 210 {\mu}m. Together with the results from ground-based observations, these spatially resolved data can be modelled to determine the nature of the debris and its evolution more reliably than would be possible from unresolved data alone. For the first time has the q1 Eri disc been resolved at far infrared wavelengths. The PACS observations at 70, 100 and 160 {\mu}m reveal an oval image showing a disc-like structure in all bands, the size of which increases with wavelength. Assuming a circular shape yields the inclination of its equatorial plane with respect to that of the sky, i > 53deg. The results of image de-convolution indicate that i likely is larger than 63deg, where 90deg corresponds to an edge-on disc. {abridged}, Comment: 5 pages, 3 figures

We summarize the first results from the Gould Belt survey, obtained toward the Aquila Rift and Polaris Flare regions during the 'science demonstration phase' of Herschel. Our 70-500 micron images taken in parallel mode with the SPIRE and PACS cameras reveal a wealth of filamentary structure, as well as numerous dense cores embedded in the filaments. Between ~ 350 and 500 prestellar cores and ~ 45-60 Class 0 protostars can be identified in the Aquila field, while ~ unbound starless cores and no protostars are observed in the Polaris field. The prestellar core mass function (CMF) derived for the Aquila region bears a strong resemblance to the stellar initial mass function (IMF), already confirming the close connection between the CMF and the IMF with much better statistics than earlier studies. Comparing and contrasting our Herschel results in Aquila and Polaris, we propose an observationally-driven scenario for core formation according to which complex networks of long, thin filaments form first within molecular clouds, and then the densest filaments fragment into a number of prestellar cores via gravitational instability., Comment: 7 pages, 4 figures. Accepted for publication in Astronomy and Astrophysics, Herschel Special Issue

We present Herschel observations of the isolated, low-mass star-forming Bok globule CB244. It contains two cold sources, a low-mass Class 0 protostar and a starless core, which is likely to be prestellar in nature, separated by 90 arcsec (~ 18000 AU). The Herschel data sample the peak of the Planck spectrum for these sources, and are therefore ideal for dust-temperature and column density modeling. With these data and a near-IR extinction map, the MIPS 70 micron mosaic, the SCUBA 850 micron map, and the IRAM 1.3 mm map, we model the dust-temperature and column density of CB244 and present the first measured dust-temperature map of an entire star-forming molecular cloud. We find that the column-averaged dust-temperature near the protostar is ~ 17.7 K, while for the starless core it is ~ 10.6K, and that the effect of external heating causes the cloud dust-temperature to rise to ~ 17 K where the hydrogen column density drops below 10^21 cm^-2. The total hydrogen mass of CB244 (assuming a distance of 200 pc) is 15 +/- 5 M_sun. The mass of the protostellar core is 1.6 +/- 0.1 M_sun and the mass of the starless core is 5 +/- 2 M_sun, indicating that ~ 45% of the mass in the globule is participating in the star-formation process., Comment: Accepted for A&A Herschel Special Issue; 5 pages, 2 figures

We present the results of a comprehensive infrared, submillimetre, and millimetre continuum emission study of isolated low-mass star-forming cores in 32 Bok globules, with the aim to investigate the process of star formation in these regions. The submillimetre and millimetre dust continuum emission maps together with the spectral energy distributions are used to model and derive the physical properties of the star-forming cores, such as luminosities, sizes, masses, densities, etc. Comparisons with ground-based near-infrared and space-based mid and far-infrared images from Spitzer are used to reveal the stellar content of the Bok globules, association of embedded young stellar objects with the submm dust cores, and the evolutionary stages of the individual sources. Submm dust continuum emission was detected in 26 out of the 32 globule cores observed. For 18 globules with detected (sub)mm cores we derive evolutionary stages and physical parameters of the embedded sources. We identify nine starless cores, most of which are presumably prestellar, nine Class 0 protostars, and twelve Class I YSOs. Specific source properties like bolometric temperature, core size, and central densities are discussed as function of evolutionary stage. We find that at least two thirds (16 out of 24) of the star-forming globules studied here show evidence of forming multiple stars on scales between 1,000 and 50,000 AU. However, we also find that most of these small prototstar and star groups are comprised of sources with different evolutionary stages, suggesting a picture of slow and sequential star formation in isolated globules, Comment: 60 pages, 28 figures, accepted by The Astrophysical Journal Supplement Series

We studied several representative circumstellar disks surrounding the Herbig Ae star MWC 480 and the T Tauri stars LkCa 15 and DM Tau at (sub-)millimeter wavelengths in lines of CCH. Our aim is to characterize photochemistry in the heavily UV-irradiated MWC 480 disk and compare the results to the disks around cooler T Tauri stars. We detected and mapped CCH in these disks with the IRAM Plateau de Bure Interferome- ter in the C- and D-configurations in the (1-0) and (2-1) transitions. Using an iterative minimization technique, the CCH column densities and excitation conditions are con- strained. Very low excitation temperatures are derived for the T Tauri stars. These values are compared with the results of advanced chemical modeling, which is based on a steady-state flared disk structure with a vertical temperature gradient, and a gas- grain chemical network with surface reactions. Both model and observations suggest that CCH is a sensitive tracer of the X-ray and UV irradiation. The predicted radial dependency and source to source variations of CCH column densities qualitatively agree with the observed values, but the predicted column densities are too low by a factor of several. The chemical model fails to reproduce high concentrations of CCH in very cold disk midplane as derived from the observed low excitation condition for both the (1-0) and (2-1) transitions., Comment: 23 pages, 9 figures, 3 tables, accepted for publication in ApJ