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Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun from the Gaia Early Data Release 3. We characterise the catalogue through comparisons to the full data release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use., Methods. Theselection of objects within 100 pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100 pc is included in the catalogue., Results. We have produced a catalogue of 331 312 objects that we estimate contains at least 92% of stars of stellar type M9 within 100 pc of the Sun. We estimate that 9% of the stars in this catalogue probably lie outside 100 pc, but when the distance probability function is used, a correct treatment of this contamination is possible. We produced luminosity functions with a high signal-to-noise ratio for the main-sequence stars, giants, and white dwarfs. We examined in detail the Hyades cluster, the white dwarf population, and wide-binary systems and produced candidate lists for all three samples. We detected local manifestations of several streams, superclusters, and halo objects, in which we identified 12 members of Gaia Enceladus. We present the first direct parallaxes of five objects in multiple systems within 10 pc of the Sun., Conclusions. We provide the community with a large, well-characterised catalogue of objects in the solar neighbourhood. This is a primary benchmark for measuring and understanding fundamental parameters and descriptive functions in astronomy.

Aims. We aim to demonstrate the scientific potential of the Gaia Early Data Release 3 (EDR3) for the study of different aspects of the Milky Way structure and evolution and we provide, at the same time, a description of several practical aspects of the data and examples of their usage., Methods. We used astrometric positions, proper motions, parallaxes, and photometry from EDR3 to select different populations and components and to calculate the distances and velocities in the direction of the anticentre. In this direction, the Gaia astrometric data alone enable the calculation of the vertical and azimuthal velocities; also, the extinction is relatively low compared to other directions in the Galactic plane. We then explore the disturbances of the current disc, the spatial and kinematical distributions of early accreted versus in situ stars, the structures in the outer parts of the disc, and the orbits of open clusters Berkeley 29 and Saurer 1., Results. With the improved astrometry and photometry of EDR3, we find that: (i) the dynamics of the Galactic disc are very complex with oscillations in the median rotation and vertical velocities as a function of radius, vertical asymmetries, and new correlations, including a bimodality with disc stars with large angular momentum moving vertically upwards from below the plane, and disc stars with slightly lower angular momentum moving preferentially downwards; (ii) we resolve the kinematic substructure (diagonal ridges) in the outer parts of the disc for the first time; (iii) the red sequence that has been associated with the proto-Galactic disc that was present at the time of the merger with Gaia-Enceladus-Sausage is currently radially concentrated up to around 14 kpc, while the blue sequence that has been associated with debris of the satellite extends beyond that; (iv) there are density structures in the outer disc, both above and below the plane, most probably related to Monoceros, the Anticentre Stream, and TriAnd, for which the Gaia data allow an exhaustive selection of candidate member stars and dynamical study; and (v) the open clusters Berkeley 29 and Saurer 1, despite being located at large distances from the Galactic centre, are on nearly circular disc-like orbits., Conclusions. Even with our simple preliminary exploration of the Gaia EDR3, we demonstrate how, once again, these data from the European Space Agency are crucial for our understanding of the different pieces of our Galaxy and their connection to its global structure and history.

Context. Gaia Early Data Release 3 (Gaia EDR3) provides accurate astrometry for about 1.6 million compact (QSO-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions., Aims. The proper motions of QSO-like sources are used to reveal a systematic pattern due to the acceleration of the solar systembarycentre with respect to the rest frame of the Universe. Apart from being an important scientific result by itself, the acceleration measured in this way is a good quality indicator of the Gaia astrometric solution., Methods. Theeffect of the acceleration was obtained as a part of the general expansion of the vector field of proper motions in vector spherical harmonics (VSH). Various versions of the VSH fit and various subsets of the sources were tried and compared to get the most consistent result and a realistic estimate of its uncertainty. Additional tests with the Gaia astrometric solution were used to get a better idea of the possible systematic errors in the estimate., Results. Our best estimate of the acceleration based on Gaia EDR3 is (2.32 +/- 0.16) x 10(-10) m s(-2) (or 7.33 +/- 0.51 km s(-1) Myr-1) towards alpha = 269.1 degrees +/- 5.4 degrees, delta = -31.6 degrees +/- 4.1 degrees, corresponding to a proper motion amplitude of 5.05 +/- 0.35 mu as yr(-1). This is in good agreement with the acceleration expected from current models of the Galactic gravitational potential. We expect that future Gaia data releases will provide estimates of the acceleration with uncertainties substantially below 0.1 mu as yr(-1).

Aims.We aim to determine far-infrared fluxes at 70, 100, and 160μm for the five major Uranus satellites, Titania, Oberon, Umbriel, Ariel, and Miranda. Our study is based on the available calibration observations at wavelengths taken with the PACS photometer aboard theHerschelSpace Observatory.Methods.The bright image of Uranus was subtracted using a scaled Uranus point spread function (PSF) reference established from all maps of each wavelength in an iterative process removing the superimposed moons. The photometry of the satellites was performed using PSF photometry. Thermophysical models of the icy moons were fitted to the photometry of each measurement epoch and auxiliary data at shorter wavelengths.Results.The best-fit thermophysical models provide constraints for important properties of the moons, such as surface roughness and thermal inertia. We present the first thermal infrared radiometry longward of 50μm for the four largest Uranian moons, Titania, Oberon, Umbriel, and Ariel, at epochs with equator-on illumination. Due to this inclination geometry, heat transport took place to the night side so that thermal inertia played a role, allowing us to constrain that parameter. Also, we found some indication for differences in the thermal properties of leading and trailing hemispheres. The total combined flux contribution of the four major moons relative to Uranus is 5.7 × 10−3, 4.8 × 10−3, and 3.4 × 10−3at 70, 100, and 160μm, respectively. We therefore precisely specify the systematic error of the Uranus flux by its moons when Uranus is used as a far-infrared prime flux calibrator. Miranda is considerably fainter and always close to Uranus, impeding reliable photometry.Conclusions.We successfully demonstrate an image processing technique for PACS photometer data that allows us to remove a bright central source and reconstruct point source fluxes on the order of 10−3of the central source as close as ≈3 × the half width at half maximum of the PSF. We established improved thermophysical models of the five major Uranus satellites. Our derived thermal inertia values resemble those of trans-neptunian object (TNO) dwarf planets, Pluto and Haumea, more than those of smaller TNOs and Centaurs at heliocentric distances of about 30 AU.

We present multi-epoch optical and near-infrared (NIR) photometry and spectroscopy of the spectroscopic binary T Tauri star DQ Tau. The photometric monitoring, obtained using SMARTS ANDICAM, recovers the previously-seen correlation between optical flux and the 15.8-day binary orbital period, with blue flux peaks occurring close to most observed periastron passages. For the first time, we find an even more consistent correlation between orbital period and NIR brightness and color. The onset of pulse events in the NIR on average precedes those in the optical by a few days, with the rise usually starting near apastron orbital phase. We further obtained five epochs of spectroscopy using IRTF SpeX, with a wavelength range of 0.8 to 5 microns, and derived spectra of the infrared excess emission. The shape and strength of the excess varies with time, with cooler and weaker characteristic dust emission (T ~ 1100-1300 K) over most of the binary orbit, and stronger/warmer dust emission (T ~ 1600 K, indicative of dust sublimation) just before periastron passage. We suggest our results are broadly consistent with predictions of simulations of disk structure and accretion flows around close binaries, with the varying dust emission possibly tracing the evolution of accretion streams falling inwards through a circumbinary disk cavity and feeding the accretion pulses traced by the optical photometry and NIR emission lines. However, our results also show more complicated behavior that is not fully explained by this simple picture, and will require further observations and modeling to fully interpret., Comment: accepted to ApJ

2007 OR10 is currently the third largest known dwarf planet in the trans-Neptunian region, with an effective radiometric diameter of ∼1535 km. It has a slow rotation period of ∼45 hr that was suspected to be caused by tidal interactions with a satellite undetected at that time. Here, we report on the discovery of a likely moon of 2007 OR10, identified on archival Hubble Space Telescope WFC3/UVIS system images. Although the satellite is detected at two epochs, this does not allow an unambiguous determination of the orbit and the orbital period. A feasible 1.5-5.8 • 1021 kg estimate for the system mass leads to a likely 35-100 day orbital period. The moon is about 4.2 fainter than 2007 OR10 in HST images that corresponds to a diameter of 237 km assuming equal albedos with the primary. Due to the relatively small size of the moon, the previous size and albedo estimates for the primary remains unchanged. With this discovery all trans-Neptunian objects larger than 1000 km are now known to harbor satellites, an important constraint for moon formation theories in the young solar system. © 2017. The American Astronomical Society. All rights reserved., The research leading to these results has received funding from the European Unions Horizon 2020 Research and Innovation Programme, under Grant Agreement No. 687378; from the GINOP-2.3.2-15-2016-00003 grant of the National Research, Development and Innovation Office (Hungary); and from the LP2012-31 grant of the Hungarian Academy of Sciences. Funding from Spanish grant AYA-2014-56637-C21-P is acknowledged, as is the Proyecto de Excelencia de la Junta de Andaluca, J.A. 2012-FQM1776.

The absolute stability of the PACS bolometer response over the entire mission lifetime without applying any corrections is about 0.5% (standard deviation) or about 8% peak-to-peak. This fantastic stability allows us to calibrate all scientific measurements by a fixed and time-independent response file, without using any information from the PACS internal calibration sources. However, the analysis of calibration block observations revealed clear correlations of the internal source signals with the evaporator temperature and a signal drift during the first half hour after the cooler recycling. These effects are small, but can be seen in repeated measurements of standard stars. From our analysis we established corrections for both effects which push the stability of the PACS bolometer response to about 0.2% (stdev) or 2% in the blue, 3% in the green and 5% in the red channel (peak-to-peak). After both corrections we still see a correlation of the signals with PACS FPU temperatures, possibly caused by parasitic heat influences via the Kevlar wires which connect the bolometers with the PACS Focal Plane Unit. No aging effect or degradation of the photometric system during the mission lifetime has been found., 15 pages, accepted for publication in Experimental Astronomy

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

Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about a month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster whose low declination makes it observable by the Spitzer space telescope over a 200 day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find such variability is common, occurring in ~80% of the detected cluster members. The change in [3.6]-[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200 day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ~0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic., Comment: Accepted to ApJ

We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (~ 6 - 10 Myr old), relatively nearby (800 pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope, covering the wavelength range from 3.6 to 24 microns. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii ~ 0.1 to ~ 10AU from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from ~ 1 to ~ 18 Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24 micron excesses ([8] - [24] > 1.5) increases from 8.4 +\- 1.3% at ~ 3 Myr to 46 +\- 5% at ~ 10 Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend., accepted by the Astrophysical Journal

Aims: Our aims are to determine flux densities and their photometric accuracy for a set of seventeen stars that range in flux from intermediately bright (≲2.5 Jy) to faint (≳5 mJy) in the far- infrared (FIR). We also aim to derive signal-to-noise dependence with flux and time, and compare the results with predictions from the Herschel exposure-time calculation tool. Methods: We obtain aperture photometry from Herschel-PACS high-pass-filtered scan maps and chop/nod observations of the faint stars. The issues of detection limits and sky confusion noise are addressed by comparison of the field-of-view at different wavelengths, by multi-aperture photometry, by special processing of the maps to preserve extended emission, and with the help of large-scale absolute sky brightness maps from AKARI. This photometry is compared with flux-density predictions based on photospheric models for these stars. We obtain a robust noise estimate by fitting the flux distribution per map pixel histogram for the area around the stars, scaling it for the applied aperture size and correcting for noise correlation. Results: For 15 stars we obtain reliable photometry in at least one PACS filter, and for 11 stars we achieve this in all three PACS filters (70, 100, 160 μm). Faintest fluxes, for which the photometry still has good quality, are about 10-20 mJy with scan map photometry. The photometry of seven stars is consistent with models or flux predictions for pure photospheric emission, making them good primary standard candidates. Two stars exhibit source-intrinsic far- infrared excess: β Gem (Pollux), being the host star of a confirmed Jupiter-size exoplanet, due to emission of an associated dust disk, and η Dra due to dust emission in a binary system with a K1 dwarf. The investigation of the 160 μm sky background and environment of four sources reveals significant sky confusion prohibiting the determination of an accurate stellar flux at this wavelength. As a good model approximation, for nine stars we obtain scaling factors of the continuum flux models of four PACS fiducial standards with the same or quite similar spectral type. We can verify a linear dependence of signal-to- noise ratio (S/N) with flux and with square root of time over significant ranges. At 160 μm the latter relation is, however, affected by confusion noise. Conclusions: The PACS faint star sample has allowed a comprehensive sensitivity assessment of the PACS photometer. Accurate photometry allows us to establish a set of five FIR primary standard candidates, namely α Ari, ∊ Lep, ω Cap, HD 41047 and 42 Dra, which are 2-20 times fainter than the faintest PACS fiducial standard (γ Dra) with absolute accuracy of http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/613/A40

Globular clusters have proven to be essential to our understanding of many important astrophysical phenomena. Here we analyse spectroscopic observations of ten Halo globular clusters to determine their dark matter content, their tidal heating by the Galactic disc and halo, describe their metallicities and the likelihood that Newtonian dynamics explain their kinematics. We analyse a large number of members in all clusters, allowing us to address all these issues together, and we have included NGC 288 and M30 to overlap with previous studies. We find that any flattening of the velocity dispersion profiles in the outer regions of our clusters can be explained by tidal heating. We also find that all our GCs have M/L_V < 5, therefore, we infer the observed dynamics do not require dark matter, or a modification of gravity. We suggest that the lack of tidal heating signatures in distant clusters indicates the Halo is not triaxial. The isothermal rotations of each cluster are measured, with M4 and NGC 288 exhibiting rotation at a level of 0.9 +/- 0.1 km/s and 0.25 +/- 0.15 km/s, respectively. We also indirectly measure the tidal radius of NGC 6752, determining a more realistic figure for this cluster than current literature values. Lastly, an unresolved and intriguing puzzle is uncovered with regard to the cooling of the outer regions of all ten clusters.

We present and discuss \emph{Spitzer} and near-infrared H$_{2}$ observations of a new bi-polar protostellar outflow in the Rosette Molecular Cloud. The outflow is seen in all four IRAC bands and partially as diffuse emission in the MIPS 24 $\mu$m band. An embedded MIPS 24 $\mu$m source bisects the outflow and appears to be the driving source. This source is coincident with a dark patch seen in absorption in the 8 $\mu$m IRAC image. \emph{Spitzer} IRAC color analysis of the shocked emission was performed from which thermal and column density maps of the outflow were constructed. Narrow-band near-infrared (NIR) images of the flow reveal H$_2$ emission features coincident with the high temperature regions of the outflow. This outflow has now been given the designation MHO 1321 due to the detection of NIR H$_2$ features. We use these data and maps to probe the physical conditions and structure of the flow., Comment: Accepted for publication in The Astrophysical Journal

We present results of optical spectroscopic and BVR_CI_C photometric observations of 77 pre-main sequence (PMS) stars in the Cepheus flare region. A total of 64 of these are newly confirmed PMS stars, originally selected from various published candidate lists. We estimate effective temperatures and luminosities for the PMS stars, and comparing the results with pre-main sequence evolutionary models we estimate stellar masses of 0.2-2.4M_sun and stellar ages of 0.1-15 Myr. Among the PMS stars, we identify 15 visual binaries with separations of 2-10 arcsec. From archival IRAS, 2MASS, and Spitzer data, we construct their spectral energy distributions and classify 5% of the stars as Class I, 10% as Flat SED, 60% as Class II, and 3% as Class III young stellar objects (YSOs). We identify 12 CTTS and 2 WTTS as members of NGC 7023, with mean age of 1.6 Myr. The 13 PMS stars associated with L1228 belong to three small aggregates: RNO 129, L1228A, and L1228S. The age distribution of the 17 PMS stars associated with L1251 suggests that star formation has propagated with the expansion of the Cepheus flare shell. We detect sparse aggregates of 6-7 Myr old PMS stars around the dark clouds L1177 and L1219, at a distance of 400 pc. Three T Tauri stars appear to be associated with the Herbig Ae star SV Cep at a distance of 600 pc. Our results confirm that the molecular complex in the Cepheus flare region contains clouds of various distances and star forming histories., 61 pages, 27 figures, 8 tables; accepted for publication by ApJS

We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 micron shadows. The Spitzer images show 8 and 24 micron shadows and in some cases 70 micron shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a 12CO (2-1) and 13CO (2-1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 micron shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freeze--out onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion we find that ~ 2/3 of the cores selected to have prominent 24 micron shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 micron shadows. All cores observed to produce absorption features at 70 micron are close to collapse. We conclude that 24 micron shadows, and even more so the 70 micron ones, are useful markers of cloud cores that are approaching collapse.

We present multi-epoch Spitzer Space Telescope observations of the transitional disk LRLL 31 in the 2-3 Myr-old star forming region IC 348. Our measurements show remarkable mid-infrared variability on timescales as short as one week. The infrared continuum emission exhibits systematic wavelength-dependent changes that suggest corresponding dynamical changes in the inner disk structure and variable shadowing of outer disk material. We propose several possible sources for the structural changes, including a variable accretion rate or a stellar or planetary companion embedded in the disk. Our results indicate that variability studies in the infrared can provide important new constraints on protoplanetary disk behavior., 15 pages, 4 figures, accepted to ApJ Letters

We present a Spitzer IRAC and MIPS survey of NGC 2451 A and B, two open clusters in the 50-80 Myr age range. We complement these data with extensive ground-based photometry and spectroscopy to identify the cluster members in the Spitzer survey field. We find only two members with 8 micron excesses. The incidence of excesses at 24 microns is much higher, 11 of 31 solar-like stars and 1 of 7 early-type (A) stars. This work nearly completes the debris disk surveys with Spitzer of clusters in the 30-130 Myr range. This range is of inte rest because it is when large planetesimal collisions may have still been relatively common (as indicated by the one that led to the formation of the Moon during this period of the evolution of the Solar System). We review the full set of surveys and find that there are only three possible cases out of about 250 roughly solar-mass stars where very large excesses suggest that such collisions have occurred recently., Comment: Accepted for publication in ApJ. 25 pages 17 figures

We report the outcome of a deep multi-wavelength study of the IC2391 young open cluster. We aim at uncovering new low-mass and sub-stellar members of the cluster and identifying new debris disk objects. A 30*30 square arcmin area in IC 2391 was observed using the wide-field imager at the ESO 2.2m telescope. The completeness limits of the photometry at 3 sigma level are V=24.7, Rc=23.7 and Ic=23.0, faint enough to reveal sub-stellar members down to about 0.03 solar masses. Our membership criteria are based on the use of our optical data, in combination with JHKs magnitudes from the 2MASS catalog. We also estimate the physical parameters of the selected candidates. Debris disk candidates are identified on the basis of their infrared excess emission using near- and mid-infrared photometry from the Spitzer Space Telescope. Our optical survey, which has a limiting magnitude at 3 sigma level 1-2 mag fainter than previous optical surveys conducted in IC2391, revealed 29 new low-mass member candidates of the cluster. We estimate the contamination to be at least 50%. We constrain the fraction of sub-stellar objects in the range 8-15% and discuss possible explanations for the deficit of brown dwarfs in this cluster. We also identified 10 candidates in the cluster showing IR excess emission consistent with the presence of debris disks., Comment: 17 pages, 9 figures

We present a 1.5deg x 8deg (220pc x 1195pc) Multiband Imaging Photometer for Spitzer 24um image of the Galactic Center and an accompanying point source list. This image is the highest spatial resolution (6" ~ 0.25pc) and sensitivity map ever taken across the GC at this wavelength, showing the emission by warm dust in unprecedented detail. Over 120,000 point sources are identified in this catalog with signal-to-noise ratios greater than five and flux densities from 0.6mJy to 9Jy., Comment: 10 pages, 5 figures, accepted to ApJS, full catalog and color Fig 1 available upon request to first author

We present results of optical spectroscopic and photometric observation of the pre-main sequence stars associated with the cometary shaped dark cloud Lynds 1622, and 12CO and 13CO observations of the cloud. We determined the effective temperatures and luminosities of 14 pre-main sequence stars associated with the cloud from their positions in the Hertzsprung--Russell diagram, as well as constructed their spectral energy distributions using optical, 2MASS and Spitzer IRAC and MIPS data. We derived physical parameters of L1622 from the molecular observations. Our results are not compatible with the assumption that L1622 lies on the near side of the Orion-Eridanus loop, but suggest that L1622 is as distant as Orion B. At a distance of 400 pc the mass of the cloud, derived from our CO data, is 1100 solar masses, its star formation efficiency is 1.8%, and the average age of its low-mass pre-main sequence star population is about 1 million years., Comment: 13 pages, 9 figures, 4 tables; accepted by MNRAS

We have surveyed the 30 Myr-old cluster NGC 2547 for planetary debris disks using Spitzer. At 4.5-8 um we are sensitive to the photospheric level down to mid-M stars (0.2 Msol) and at 24 um to early-G stars (1.2 Msol). We find only two to four stars with excesses at 8 um out of ~400-500 cluster members, resulting in an excess fraction, Comment: Accepted to ApJ, 29 pages, 13 figs. A Note in Proof concerning cluster's age was added in the original submission of 2007 July 19. Full Tables 1 and 2 in the electronic form together with the article with full resolution figures are available at http://www.astro.ufl.edu/~ngorlova/disksNGC2547/

We present Spitzer observations of the dark globule CB190 (L771). We observe a roughly circular 24 micron shadow with a 70 arcsec radius. The extinction profile of this shadow matches the profile derived from 2MASS photometry at the outer edges of the globule and reaches a maximum of ~32 visual magnitudes at the center. The corresponding mass of CB190 is ~10 Msun. Our 12CO and 13CO J = 2-1 data over a 10 arcmin X 10 arcmin region centered on the shadow show a temperature ~10 K. The thermal continuum indicates a similar temperature for the dust. The molecular data also show evidence of freezeout onto dust grains. We estimate a distance to CB190 of 400 pc using the spectroscopic parallax of a star associated with the globule. Bonnor-Ebert fits to the density profile, in conjunction with this distance, yield xi_max = 7.2, indicating that CB190 may be unstable. The high temperature (56 K) of the best fit Bonnor-Ebert model is in contradiction with the CO and thermal continuum data, leading to the conclusion that the thermal pressure is not enough to prevent free-fall collapse. We also find that the turbulence in the cloud is inadequate to support it. However, the cloud may be supported by the magnetic field, if this field is at the average level for dark globules. Since the magnetic field will eventually leak out through ambipolar diffusion, it is likely that CB190 is collapsing or in a late pre-collapse stage., 16 pages, 13 figures, accepted for publication in ApJ

We analyze 8 sources with strong mid-infrared excesses in the 13 Myr-old double cluster h and chi Persei. New optical spectra and broadband SEDs (0.36-8 mu_m) are consistent with cluster membership. We show that material with T ~ 300-400 K and Ld/Lstar ~ 10^-4-10^-3 produces the excesses in these sources. Optically-thick blackbody disk models - including those with large inner holes - do not match the observed SEDs. The SEDs of optically-thin debris disks produced from terrestrial planet formation calculations match the observations well. Thus, some h and chi Persei stars may have debris from terrestrial zone planet formation., 5 pages, 3 figures, Matched to published version, Astrophysical Journal Letters, in press: 2007, ApJL, 663, 105

We describe IRAC 3.6-8 mu_m observations and ground-based near-IR JHKs photometry from Mimir and 2MASS of the massive double cluster h & chi Persei complete to J=15.5 (M ~ 1.3 Msun. Within 25' of the cluster centers we detect \~11,000 sources with J < 15.5, ~7,000 sources with [4.5] < 15, and ~ 5000 sources with [8] < 14.5. In both clusters, the surface density profiles derived from the 2MASS data decline with distance from the cluster centers as expected for a bound cluster. Within 15' of the cluster centers, ~ 50% of the stars lie on a reddened ~ 13 Myr isochrone; at 15'-25' from the cluster centers, ~ 40% lie on this isochrone. Thus, the optical/2MASS color-magnitude diagrams indicate that h & chi Per are accompanied by a halo population with roughly the same age and distance as the two dense clusters. The double cluster lacks any clear IR excess sources for J < 13.5 (~ 2.7 Msun). Therefore, disks around high-mass stars disperse prior to ~ 10^{7} yr. At least 2-3% of the fainter cluster stars have strong IR excess at both [5.8] and [8]. About 4-8% of sources slightly more massive than the Sun (~ 1.4 Msun) have IR excesses at [8]. Combined with the lack of detectable excesses for brighter stars, this result suggests that disks around lower-mass stars have longer lifetimes. The IR excess population also appears to be larger at longer IRAC bands ([5.8], [8]) than at shorter IRAC/2MASS bands ($K_{s}$, [4.5]), a result consistent with an inside-out clearing of disks., Comment: matched to published version, 26 pages, 18 figures: 2007, ApJ, 659, 599

Debris disks are considered to be gas-poor, but recent observations revealed molecular or atomic gas in several 10-40 Myr old systems. We used the APEX and IRAM 30m radiotelescopes to search for CO gas in 20 bright debris disks. In one case, around the 16 Myr old A-type star HD 131835, we discovered a new gas-bearing debris disk, where the CO 3-2 transition was successfully detected. No other individual system exhibited a measurable CO signal. Our Herschel Space Observatory far-infrared images of HD 131835 marginally resolved the disk both at 70 and 100$\mu$m, with a characteristic radius of ~170 au. While in stellar properties HD 131835 resembles $\beta$ Pic, its dust disk properties are similar to those of the most massive young debris disks. With the detection of gas in HD 131835 the number of known debris disks with CO content has increased to four, all of them encircling young ($\leq$40 Myr) A-type stars. Based on statistics within 125 pc, we suggest that the presence of detectable amount of gas in the most massive debris disks around young A-type stars is a common phenomenon. Our current data cannot conclude on the origin of gas in HD 131835. If the gas is secondary, arising from the disruption of planetesimals, then HD 131835 is a comparably young and in terms of its disk more massive analogue of the $\beta$ Pic system. However, it is also possible that this system similarly to HD 21997 possesses a hybrid disk, where the gas material is predominantly primordial, while the dust grains are mostly derived from planetesimals., Comment: Accepted for publication in ApJ, 18 pages, 9 figures, 5 tables

From a long time series of high resolution (R=115,000) HARPS spectra and simultaneous broad-band photometry, we report new evidence for magnetospheric accretion as well as ejection processes in the nearly edge-on classical T Tauri star AA Tau. AA Tau's light curve is modulated with a period of 8.22d. The recurrent luminosity dips are due to the periodic occultation of the central star by the magnetically-warped inner disk edge located at about 9 Rstar. Balmer line profiles exhibit a clear rotational modulation of high-velocity redshifted absorption components with a period of 8.22 days as well, with a maximum strength when the main accretion funnel flow passes through the line of sight. At the same time, the luminosity of the system decreases by about 1 mag, indicative of circumstellar absorption of the stellar photosphere by the magnetically-warped, corotating inner disk edge. The photospheric and HeI radial velocities also exhibit periodic variations, and the veiling is modulated by the appearance of the accretion shock at the bottom of the accretion funnel. Diagnostics of hot winds and their temporal behaviour are also presented. The peculiar geometry of the young AA Tau system (nearly edge-on) allows us to uniquely probe the acretion-ejection region close to the star. We find that most spectral and photometric diagnostics vary as expected from models of magnetically-channelled accretion in young stars, with a large scale magnetosphere tilted by 20 deg onto the star's spin axis. We also find evidence for time variability of the magnetospheric accretion flow on a timescale of a few rotational periods., Comment: 14 pages

Medium-resolution optical spectroscopy of the candidate YSOs associated with the small, nearby molecular cloud Lynds~1333 revealed four previously unknown classical T Tauri stars, two of which are components of a visual double, and a Class I source, IRAS 02086+7600. The spectroscopic data, together with new V,R_ C,I_C photometric and 2MASS J, H, and K_s data allowed us to estimate the masses and ages of the new T Tauri stars. We touch on the possible scenario of star formation in the region. L1333 is one of the smallest and nearest known star forming clouds, therefore it may be a suitable target for studying in detail the small scale structure of a star forming environment., Comment: 7 pages, 4 figures, accepted by MNRAS

Periodic increases in luminosity arising from variable accretion rates have been predicted for some close pre-main sequence binary stars as they grow from circumbinary disks. The phenomenon is known as "pulsed accretion" and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation in the circumbinary environment. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from 0-50 percent from orbit to orbit. Here we report on a young protostar (age ~10^5 yr) that exhibits periodic variability in which the infrared luminosity increases by a factor of 10 in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied., Comment: 25 pages, 9 figures

We describe the results of two near infrared (K-band) imaging surveys and a three color (JHK) survey of the vicinity of NGC 7538. The limiting magnitudes are K ~ 16.5 and K ~ 17.5 mag for the K-band surveys and K ~ 15 mag for the JHK survey. We identify more than 2000 and 9000 near-infrared (NIR) sources on the images of the two K-band surveys and 786 NIR sources in the JHK survey. From color-color diagrams, we derive a reddening law for background stars and identify 238 stars with NIR excesses. Contour maps indicate a high density peak coincident with a concentration of stars with NIR excesses. We identify this peak as a young, embedded cluster and confirm this result with the K-band luminosity function, color histograms, and color-magnitude diagrams. The center of the cluster is at RA = 23:13:39.34, DEC = 61:29:18.9. The cluster radius is $\sim$ 3' ~ 2.5 pc for an adopted distance, d ~ 2.8 kpc. For d = 2.8 kpc, and reddening, E_{J-K} = 0.55 mag, the slope of the logarithmic K-band luminosity function (KLF) of the cluster, s ~ 0.32 +- 0.03, agrees well with previous results for L1630 (s = 0.34) and M17 (s = 0.26)., Comment: 26 pages with 11 figures. Accepted by Astronomical Journal

HD 95086 is a young early-type star that hosts (1) a 5 MJ planet at the projected distance of 56 AU revealed by direct imaging, and (2) a prominent debris disk. Here we report the detection of 69 um crystalline olivine feature from the disk using the Spitzer/MIPS-SED data covering 55-95 um. Due to the low resolution of MIPS-SED mode, this feature is not spectrally resolved, but is consistent with the emission from crystalline forsterite contributing 5% of the total dust mass. We also present detailed analysis of the disk SED and re-analysis of resolved images obtained by Herschel. Our results suggest that the debris structure around HD 95086 consists of a warm (175 K) belt, a cold (55 K) disk, and an extended disk halo (up to 800 AU), and is very similar to that of HR 8799. We compare the properties of the three debris components, and suggest that HD 95086 is a young analog of HR 8799. We further investigate and constrain single-planet, two-planet, three-planet and four-planet architectures that can account for the observed debris structure and are compatible with dynamical stability constraints. We find that equal-mass four-planet configurations of geometrically spaced orbits, with each planet of mass 5 MJ, could maintain the gap between the warm and cold debris belts, and also be just marginally stable for timescales comparable to the age of the system., Comment: accepted for publication in ApJ

CCD photometry in Johnson UBV and Stromgren uvby systems and medium-resolution spectroscopy of the galactic open cluster NGC 7128 are presented. Spectral types of the brightest 12 stars in the cluster field were determined based on equivalent widths of the Hα and the He i 6678-A line. The spectroscopic observations also revealed two obvious and one probable Be-type stars showing Hα emission. The analysis of the photometric diagrams gave a colour excess of E(B−V)=1.03±0.06 mag, a distance modulus DM=13.0±0.2 mag and an age above 10 Myr. Time-resolved photometric observations obtained on one night resulted in the detection of short time-scale light variations of seven new and three already known variable stars in the cluster field.

We present medium resolution spectroscopy (λ/Δλ ≈ 7,000) covering 6500-6750 Å of three emission stars in the highly reddened young open cluster NGC7128. Two of them were previously unknown. The known Be star (V1814 Cyg) is an irregular variable; one of the newly discovered stars is an eclipsing binary (V1481 Cyg) (Jerzykiewicz et al., 1996.). Physical parameters of the cluster have been determined from new UBV and uvbyHβ photometric measurements.

Recently, a new planet candidate was discovered on direct images around the young (10-17 Myr) A-type star HD95086. The strong infrared excess of the system indicates that, similarly to HR8799, {\ss} Pic, and Fomalhaut, the star harbors a circumstellar disk. Aiming to study the structure and gas content of the HD95086 disk, and to investigate its possible interaction with the newly discovered planet, here we present new optical, infrared and millimeter observations. We detected no CO emission, excluding the possibility of an evolved gaseous primordial disk. Simple blackbody modeling of the spectral energy distribution suggests the presence of two spatially separate dust belts at radial distances of 6 and 64 AU. Our resolved images obtained with the Herschel Space Observatory reveal a characteristic disk size of ~6.0x5.4 arcsec (540x490 AU) and disk inclination of ~25 degree. Assuming the same inclination for the planet candidate's orbit, its re-projected radial distance from the star is 62 AU, very close to the blackbody radius of the outer cold dust ring. The structure of the planetary system at HD95086 resembles the one around HR8799. Both systems harbor a warm inner dust belt and a broad colder outer disk and giant planet(s) between the two dusty regions. Modelling implies that the candidate planet can dynamically excite the motion of planetesimals even out to 270 AU via their secular perturbation if its orbital eccentricity is larger than about 0.4. Our analysis adds a new example to the three known systems where directly imaged planet(s) and debris disks co-exist., Comment: Accepted for publication in ApJ Letters, 6 pages, 2 figures, 3 tables (emulateapj style)

Celestial standards play a major role in observational astrophysics. They are needed to characterise the performance of instruments and are paramount for photometric calibration. During the Herschel Calibration Asteroid Preparatory Programme approximately 50 asteroids have been established as far-IR/sub-mm/mm calibrators for Herschel. The selected asteroids fill the flux gap between the sub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright calibration stars. All three Herschel instruments observed asteroids for various calibration purposes, including pointing tests, absolute flux calibration, relative spectral response function, observing mode validation, and cross-calibration aspects. Here we present newly established models for the four large and well characterized main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (21) Lutetia which can be considered as new prime flux calibrators. The relevant object-specific properties (size, shape, spin-properties, albedo, thermal properties) are well established. The seasonal (distance to Sun, distance to observer, phase angle, aspect angle) and daily variations (rotation) are included in a new thermophysical model setup for these targets. The thermophysical model predictions agree within 5% with the available (and independently calibrated) Herschel measurements. The four objects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR N-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths). Based on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel experience, the validity of these new prime calibrators ranges from mid-infrared to about 700 micron, connecting nicely the absolute stellar reference system in the mid-IR with the planet-based calibration at sub-mm/mm wavelengths., Comment: Published in Experimental Astronomy, 78 pages, 10 figures, 19 tables

Vega and Fomalhaut, are similar in terms of mass, ages, and global debris disk properties; therefore, they are often referred as "debris disk twins". We present Spitzer 10-35 um spectroscopic data centered at both stars, and identify warm, unresolved excess emission in the close vicinity of Vega for the first time. The properties of the warm excess in Vega are further characterized with ancillary photometry in the mid infrared and resolved images in the far-infrared and submillimeter wavelengths. The Vega warm excess shares many similar properties with the one found around Fomalhaut. The emission shortward of ~30 um from both warm components is well described as a blackbody emission of ~170 K. Interestingly, two other systems, eps Eri and HR 8799, also show such an unresolved warm dust using the same approach. These warm components may be analogous to the solar system's zodiacal dust cloud, but of far greater. The dust temperature and tentative detections in the submillimeter suggest the warm excess arises from dust associated with a planetesimal ring located near the water-frost line and presumably created by processes occurring at similar locations in other debris systems as well. We also review the properties of the 2 um hot excess around Vega and Fomalhaut, showing that the dust responsible for the hot excess is not spatially associated with the dust we detected in the warm belt. We suggest it may arise from hot nano grains trapped in the magnetic field of the star. Finally, the separation between the warm and cold belt is rather large with an orbital ratio >~10 in all four systems. In light of the current upper limits on the masses of planetary objects and the large gap, we discuss the possible implications for their underlying planetary architecture, and suggest that multiple, low-mass planets likely reside between the two belts in Vega and Fomalhaut., 14 pages, accepted for publication in ApJ

We explore the collisional decay of disk mass and infrared emission in debris disks. With models, we show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a slower value. The total disk mass falls off ~ t^-0.35 at its fastest point (where t is time) for our reference model, while the dust mass and its proxy -- the infrared excess emission -- fades significantly faster (~ t^-0.8). These later level off to a decay rate of M_tot(t) ~ t^-0.08 and M_dust(t) or L_ir(t) ~ t^-0.6. This is slower than the ~ t^-1 decay given for all three system parameters by traditional analytic models. We also compile an extensive catalog of Spitzer and Herschel 24, 70, and 100 micron observations. Assuming a log-normal distribution of initial disk masses, we generate model population decay curves for the fraction of debris disk harboring stars observed at 24 micron and also model the distribution of measured excesses at the far-IR wavelengths (70-100 micron) at certain age regimes. We show general agreement at 24 micron between the decay of our numerical collisional population synthesis model and observations up to a Gyr. We associate offsets above a Gyr to stochastic events in a few select systems. We cannot fit the decay in the far infrared convincingly with grain strength properties appropriate for silicates, but those of water ice give fits more consistent with the observations., Comment: 32 pages, 16 figures, emulateapj format, Accepted for publication in ApJ

(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., Accepted for publication by A&A, 21 pages (+ appendix), 21 figures

We describe extensive synoptic multi-wavelength observations of the transition disk LRLL 31 in the young cluster IC 348. We combined four epochs of IRS spectra, nine epochs of MIPS photometry, seven epochs of cold-mission IRAC photometry and 36 epochs of warm mission IRAC photometry along with multi-epoch near-infrared spectra, optical spectra and polarimetry to explore the nature of the rapid variability of this object. We find that the inner disk, as traced by the 2-5micron excess stays at the dust sublimation radius while the strength of the excess changes by a factor of 8 on weekly timescales, and the 3.6 and 4.5micron photometry shows a drop of 0.35 magnitudes in one week followed by a slow 0.5 magnitude increase over the next three weeks. The accretion rate, as measured by PaBeta and BrGamma emission lines, varies by a factor of five with evidence for a correlation between the accretion rate and the infrared excess. While the gas and dust in the inner disk are fluctuating the central star stays relatively static. Our observations allow us to put constraints on the physical mechanism responsible for the variability. The variabile accretion, and wind, are unlikely to be causes of the variability, but both are effects of the same physical process that disturbs the disk. The lack of periodicity in our infrared monitoring indicates that it is unlikely that there is a companion within ~0.4 AU that is perturbing the disk. The most likely explanation is either a companion beyond ~0.4 AU or a dynamic interface between the stellar magnetic field and the disk leading to a variable scale height and/or warping of the inner disk., Comment: Accepted to ApJ. 10 pages of text, plus 11 tables and 13 figures at the end

A long‐term observing project to determine unknown orbital periods in High Mass X‐ray Binaries (HMXB) has been underway since 2005. The primary search methods are to look for periodicities in optical light curves and in spectroscopically measured radial velocities. In the course of our searches, other non‐orbital periodicities and variations were found that likely were caused by either stellar pulsation or changes in the configuration of circumstellar dust and gas. The more unusual observations were followed up by observations with the Canadian MOST and NASA’s Spitzer space telescopes. The MOST data point to a low eccentricity orbit and a normally clump‐free circumstellar environment in the HMXB LS 5039. The Spitzer data, still preliminary, do not show any variation above systematic instrumental effects at wavelengths of 3.6 and 4.5 μm again implying a normally clump‐free circumstellar environment.

Core-collapse supernovae (CC SNe), especially Type II-Plateau ones, are thought to be important contributors to cosmic dust production. SN 2004dj, one of the closest and brightest SN since 1987A, offered a good opportunity to examine dust formation processes. To find signs of newly formed dust, we analyze all available mid-infrared (MIR) archival data from the Spitzer Space Telescope. We re-reduce and analyze data from IRAC, MIPS and IRS instruments obtained between +98 and +1381 days after explosion, generating light curves and spectra for each epoch. Observed spectral energy distributions are fitted with both analytic and numerical models, using the radiative-transfer code MOCASSIN for the latter ones. We also use imaging polarimetric data obtained at +425 days by the Hubble Space Telescope. We present convincing evidence of dust formation in the ejecta of SN 2004dj from MIR light curves and spectra. Significant MIR excess flux is detected in all bands between 3.6 and 24 um. In the optical, a ~0.8% polarization is also detected at a 2-sigma level, which exceeds the interstellar polarization in that direction. Our analysis shows that the freshly-formed dust around SN 2004dj can be modeled assuming a nearly spherical shell containing amorphous carbon grains, cooling from ~700 K to ~400 K between +267 and +1246 days. Persistent excess flux has been found above 10 um, which is explained by a cold (~115 K) dust component. If this cold dust is of circumstellar origin, it is likely to be condensed in a cool, dense shell between the forward and reverse shocks. Pre-existing circumstellar dust is less likely, but cannot be ruled out. An upper limit of ~8x10^{-4} M_sun was derived for the dust mass, which is similar to previously published values for other dust-producing SNe., Comment: 15 pages, 11 figures, 8 tables; accepted for publication in A&A; new version after minor corrections and language edition

The formation of low‐mass stars and brown dwarfs and their disks is a hot observational topic. Such studies also holds important keys for the clarification of the planet formation mechanism. Because of its proximity (150 pc) and young age (30–50 Myr), the IC2391 open cluster is an ideal location for such studies.We present the results of a deep optical survey of IC 2391 performed by using the Wide‐Field Imager at the ESO 2.2 m telescope. These data, in combination with near‐infrared photometry from 2MASS, allowed us to uncover new low‐mass members and brown dwarfs in IC 2391 and put further constrains on the shape of the low‐mass initial mass function (IMF) in this cluster, which is currently under debate. Moreover, by using data from the Spitzer space telescope, we identify a dozen of possible debris‐disk objects in the cluster and investigate their disk properties using appropriate models of circumstellar disks.

(Abridged) From photometric observations of $\sim$ 47,000 stars and spectroscopy of $\sim$ 11,000 stars, we describe the first extensive study of the stellar population of the famous Double Cluster, h and $\chi$ Persei, down to subsolar masses. Both clusters have E(B-V) $\sim$ 0.52--0.55 and dM = 11.8--11.85; the halo population, while more poorly constrained, likely has identical properties. As determined from the main sequence turnoff, the luminosity of M supergiants, and pre-main sequence isochrones, ages for h Persei, $\chi$ Persei and the halo population all converge on $\approx$ 14 Myr. From these data, we establish the first spectroscopic and photometric membership lists of cluster stars down to early/mid M dwarfs. At minimum, there are $\sim$ 5,000 members within 10' of the cluster centers, while the entire h and $\chi$ Persei region has at least $\sim$ 13,000 and as many as 20,000 members. The Double Cluster contains $\approx$ 8,400 M$_{\odot}$ of stars within 10' of the cluster centers. We estimate a total mass of at least 20,000 M$_{\odot}$. We conclude our study by outlining outstanding questions regarding the properties of h and $\chi$ Persei. From comparing recent work, we compile a list of intrinsic colors and derive a new effective temperature scale for O--M dwarfs, giants, and supergiants., Comment: 88 pages, many figures, Accepted for publication in The Astrophysical Journal Supplements. Contact lead author for version with high-resolution figures

We present new radial velocity measurements of 586 stars in a one-degree field centered on the open cluster M46, and the planetary nebula NGC 2438 located within a nuclear radius of the cluster. The data are based on medium-resolution optical and near-infrared spectra taken with the AAOmega spectrograph on the Anglo-Australian Telescope. We find a velocity difference of about 30 km/s between the cluster and the nebula, thus removing all ambiguities about the cluster membership of the planetary nebula caused by contradicting results in the literature. The line-of-sight velocity dispersion of the cluster is 3.9+/-0.3 km/s, likely to be affected by a significant population of binary stars., Comment: 6 pages + 5 figures, accepted for publication in MNRAS

We present HST/NICMOS Paschen alpha images and low and high resolution IRS spectra of photoevaporating disk-tail systems originally detected at 24 micron near O stars. We find no Paschen alpha emission in any of the systems. The resulting upper limits correspond to about 0.000002-0.000003 solar mass of mass in hydrogen in the tails suggesting that the gas is severely depleted. The IRAC data and the low resolution 5-12 micron IRS spectra provide evidence for an inner disk while high resolution long wavelength (14-30 micron) IRS spectra confirm the presence of a gas free ``tail'' that consists of ~ 0.01 to ~ 1 micron dust grains originating in the outer parts of the circumstellar disks. Overall our observations support theoretical predictions in which photoevaporation removes the gas relatively quickly (, 9 pages 5 figures, accepted for publication in ApJ

We have discovered a bow shock shaped mid-infrared excess region in front of delta Velorum using 24 micron observations obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The excess has been classified as a debris disk from previous infrared observations. Although the bow shock morphology was only detected in the 24 micron observations, its excess was also resolved at 70 micron. We show that the stellar heating of an ambient interstellar medium (ISM) cloud can produce the measured flux. Since delta Velorum was classified as a debris disk star previously, our discovery may call into question the same classification of other stars. We model the interaction of the star and ISM, producing images that show the same geometry and surface brightness as is observed. The modeled ISM is 15 times overdense relative to the average Local Bubble value, which is surprising considering the close proximity (24 pc) of delta Velorum. The abundance anomalies of lambda Bootis stars have been previously explained as arising from the same type of interaction of stars with the ISM. Low resolution optical spectra of delta Velorum show that it does not belong to this stellar class. The star therefore is an interesting testbed for the ISM accretion theory of the lambda Bootis phenomenon., Comment: 11 pages, 1 table and 13 figures, emulateapj; Accepted for publication in The Astrophysical Journal

We present UBVRI photometry of 44 type-Ia supernovae (SN Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SN Ia to date, nearly doubling the number of well-observed, nearby SN Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SN Ia observed at high redshift. The decline rate of SN Ia U-band light curves correlates well with the decline rate in other bands, as does the U-B color at maximum light. However, the U-band peak magnitudes show an increased dispersion relative to other bands even after accounting for extinction and decline rate, amounting to an additional ~40% intrinsic scatter compared to B-band., 84 authors, 71 pages, 51 tables, 10 figures. Accepted for publication in the Astronomical Journal. Version with high-res figures and electronic data at http://astron.berkeley.edu/~saurabh/cfa2snIa/

We analyze spectra of 44 emission line stars detected in a low resolution optical spectroscopic survey of the galactic open cluster NGC 6871. The survey of 1217 stars is complete to V = 14.9 and includes stars with V < 16.5 between the zero age main sequence (ZAMS) and the 10^7 yr pre-main sequence (PMS) isochrone. Of the 44 emission line stars in this survey, 28 show obvious emission in H alpha and 16 have weak H alpha absorption (compared to H gamma). We use the reddening to separate foreground and background stars from the cluster members; the position in the HR diagram (HRD) or the presence of forbidden emission lines ([NII], [SII]) then yields the evolutionary status of the emission line stars. A comparison of the H alpha spectral index distribution in NGC 6871 with the distribution of young stars in the Taurus-Auriga molecular cloud indicates that the late type PMS stars in our sample may be weak line T Tauri stars (wTTs). Many of these stars show [SII] (36%) and [NII] (45%) emission., 27 pages, 4 fiugres, 3 tables accepted for publication in Astronomical Journal

We analyze very deep IRAC and MIPS photometry of $\sim$ 12,500 members of the 14 Myr old Double Cluster, h and $\chi$ Persei, building upon on our earlier, shallower Spitzer studies (Currie et al. 2007a, 2008a). Numerous likely members show infrared (IR) excesses at 8 {\mu}m and 24 $\mu$m indicative of circumstellar dust. The frequency of stars with 8 $\mu$m excess is at least 2% for our entire sample, slightly lower (higher) for B/A stars (later type, lower-mass stars). Optical spectroscopy also identifies gas in about 2% of systems but with no clear trend between the presence of dust and gas. Spectral energy distribution (SED) modeling of 18 sources with detections at optical wavelengths through MIPS 24 $\mu m$ reveals a diverse set of disk evolutionary states, including a high fraction of transitional disks, although similar data for all disk-bearing members would provide better constraints. We combine our results with those for other young clusters to study the global evolution of dust/gas disks. For nominal cluster ages, the e-folding times ($\tau_{o}$) for the frequency of warm dust and gas are 2.75 Myr and 1.75 Myr respectively. Assuming a revised set of ages for some clusters (e.g. Bell et al. 2013), these timescales increase to 5.75 and 3.75 Myr, respectively, implying a significantly longer typical protoplanetary disk lifetime. The transitional disk duration, averaged over multiple evolutionary pathways, is $\sim$ 1 Myr. Finally, 24 $\mu$m excess frequencies for 4-6 M$_{\odot}$ stars appear lower than for 1-2.5 M$_{\odot}$ stars in other 10-30 Myr old clusters., Comment: 35 pages, 6 tables, 21 figures; Accepted for publication in The Astrophysical Journal

Variability in the infrared emission from disks around pre-main sequence stars over the course of days to weeks appears to be common, but the physical cause of the changes in disk structure are not constrained. Here we present coordinated monitoring of one young cluster with the Spitzer and Chandra space telescopes aimed at studying the physical source of the variability. In fall 2011 we obtained ten epochs of Chandra ACIS photometry over a period of 30 days with a roughly 3 day cadence contemporaneous with 20 epochs of Spitzer [3.6],[4.5] photometry over 40 days with a roughly 2 day cadence of the IC 348 cluster. This cadence allows us to search for week to month long responses of the infrared emission to changes in the high-energy flux. We find no strong evidence for a direct link between the X-ray and infrared variability on these timescales among 39 cluster members with circumstellar disks. There is no significant correlation between the shape of the infrared and X-ray light curves, or between the size of the X-ray and infrared variability. Among the stars with an X-ray flare none showed evidence of a correlated change in the infrared photometry on timescales of days to weeks following the flare. This lack of connection implies that X-ray heating of the planet forming region of the disk is not significant, although we cannot rule out rapid or instantaneous changes in infrared emission., Comment: 7 pages of text, 5 figures (+1 figure set)