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Context The Vela Molecular Ridge is one of the nearest (700 pc) giant molecular cloud (GMC) complexes hosting intermediate-mass (up to early B, late O stars) star formation, and is located in the outer Galaxy, inside the Galactic plane. Vela C is one of the GMCs making up the Vela Molecular Ridge, and exhibits both sub-regions of robust and sub-regions of more quiescent star formation activity, with both low- and intermediate(high)-mass star formation in progress. Aims We aim to study the individual and global properties of dense dust cores in Vela C, and aim to search for spatial variations in these properties which could be related to different environmental properties and/or evolutionary stages in the various sub-regions of Vela C. Methods We mapped the submillimetre (345 GHz) emission from vela C with LABOCA (beam size 19.2", spatial resolution ~0.07 pc at 700 pc) at the APEX telescope. We used the clump-finding algorithm CuTEx to identify the compact submillimetre sources. We also used SIMBA (250 GHz) observations, and Herschel and WISE ancillary data. The association with WISE red sources allowed the protostellar and starless cores to be separated, whereas the Herschel dataset allowed the dust temperature to be derived for a fraction of cores. The protostellar and starless core mass functions (CMFs) were constructed following two different approaches, achieving a mass completeness limit of 3.7 Msun. Results We retrieved 549 submillimetre cores, 316 of which are starless and mostly gravitationally bound (therefore prestellar in nature). Both the protostellar and the starless CMFs are consistent with the shape of a Salpeter initial mass function in the high-mass part of the distribution. Clustering of cores at scales of 1--6 pc is also found, hinting at fractionation of magnetised, turbulent gas., Comment: 21 pages, 19 figures, to be published in Astronomy & Astrophysics

Context. V1118 Ori is a classical EXor source whose light curve has been monitored, although not continuously, over the past 30 years. This source underwent a powerful outburst in 2005, followed by 10 years of quiescence and a less intense outburst in 2015. In 2019, a new intense brightness increase was observed (Δg ∼ 3 mag). Aims. This new accretion episode offers the opportunity to compare the photometric and spectroscopic properties of multiple outbursts of the same source. This allows us to highlight the differences and similarities among various events by removing any possible bias related to the intrinsic properties of the star-disk system. Methods. We discovered the 2019 V1118 Ori outburst by examining the g-band light curve acquired by the Zwicky Transient Facility and followed the declining phase with the Rapid Eye Mount telescope in the griz bands. Two near-infrared spectra were also acquired at different brightness stages with the Large Binocular Telescope. Results. The last event shows the following characteristics: (1) an amplitude similar to that of 2015 and lower than that of 2005; (2) a duration of less than one year as in previous events; (3) a increasing (decreasing) speed of 0.018 (0.031) mag day−1, which is different from previous cases; (4) a gradually blueing of the [g − r] color is observed over time, while the [r − i] color remains roughly unchanged; (5) with few exceptions, the near-infrared lines (mainly H I recombination) are the same as those observed in 2015; and (6) the mass accretion rate peaks at Ṁacc ∼ 10−7 M⊙ yr−1 and decreases in about a month down to a few 10−8 M⊙ yr−1. Conclusions. Our analysis shows that the comparison of data from different outbursts of the same source is a nontrivial exercise, which allows us to obtain important clues that are useful to drive theoretical efforts toward a better understanding of the EXor phenomenon.

We present the collection of all the mid- and far-IR observations (3-170 um) of the young eruptive variable PV Cep available so far in the literature. These data allow us to confirm that flux variability is a prominent feature at mid-IR wavelength (3-25 um). Color-magnitude plots clearly indicate that the observed variability is not extinction-driven, but mainly influenced by fluctuations of the mass accretion rate. We interpret such variability as due to a hot spot created onto the stellar surface by the column of accreting matter, which heats the inner parts of the disk and determines the observed increase of the near- mid-IR luminosity. A quantitative characterization is given for both the spot itself and the additional thermal component created by it. Far-IR data (60-170 um) are consistent with the presence of a temperature stratification in a massive and quite un-evolved circumstellar disk., 4 figures, accepted Astrophysics and Space Science 2014

We used the TNG/GIANO instrument to obtain near-IR high-resolution spectra (R~50000) of XZ Tau and DR Tau, two actively accreting T Tauri stars classified as EXors. The analysis of the observed features provides information on the properties of the inner disk, the accretion columns, and the winds. Both sources display composite HI line profiles, with contributions from both accreting gas and high-velocity winds. These lines become more symmetric and narrower with increasing upper energy, which may be interpreted in terms of two components with different decrements or imputed to self-absorption effects. XZ Tau shows a relatively high state of activity with respect to literature observations. The variation of the HeI 1.08um line blue-shifted absorption suggests that the inner wind has undergone a dramatic change in its velocity structure, connected with a recent accretion event. DR Tau has a more stable wind as its HeI 1.08um absorption is stable in time in spite of strong variability of the emission component. The IR veiling can be interpreted as due to blackbody emission at temperatures of 1600K for XZ Tau and 2300K DR Tau, with emitting areas ~30 times larger than the star. For XZ Tau these conditions are consistent with emission from the inner rim of the dusty disk, while for DR Tau the fairly high temperature may suggest an origin from a thick gaseous disk within the dust sublimation radius. Strong and broad metallic lines, mainly from CI and FeI, are detected in XZ Tau, similar to those observed in other EXor sources during burst phases. DR Tau shows weaker and narrower metallic lines, despite its larger accretion luminosity. This suggests that accretion is not the only driver of metallic line excitation. Our observations show the potential of wide-band, high-resolution near-IR spectroscopy to simultaneously probe the phenomena that occur in the star-disk interaction region., Comment: 15 pages, accepted by A&A

Context. EXor objects are young variables that show episodic variations of brightness commonly associated to enhanced accretion outbursts. Aims: With the aim of investigating the long-term photometric behaviour of a few EXor sources, we present here data from the archival plates of the Asiago observatory, showing the Orion field where the three EXors V1118, V1143, and NY are located. Methods: A total of 484 plates were investigated, providing a total of more than 1000 mag for the three stars, which cover a period of about 35 yr between 1959 to 1993. We then compared our data with literature data. Results: Apart from a newly discovered flare-up of V1118, we identify the same outbursts already known, but we provide two added values: (I) a long-term sampling of the quiescence phase; and (II) repeated multi-colour observations (BVRI bands). The former allows us to give a reliable characterisation of the quiescence, which represents a unique reference for studies that will analyze future outbursts and the physical changes induced by these events. The latter is useful for confirming whether the intermittent increases of brightness are accretion-driven (as in the case of V1118), or extinction-driven (as in the case of V1143). Accordingly, doubts arise about the V1143 classification as a pure EXor object. Finally, although our plates do not separate NY Ori and the star very close to it, they indicate that this EXor did not undergo any major outbursts during our 40 yr of monitoring. Full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A99

After a long-lasting period of quiescence of about a decade, the source V1118 Ori, one of the most representative members of the EXor variables, is now outbursting. Since the initial increase of the near-infrared flux of about 1 mag (JHK bands) registered on 2015 September 22, the source brightness has remained fairly stable. We estimate DeltaV about 3 mag with respect to the quiescence phase. An optical/near-IR low-resolution spectrum has been obtained with the Large Binocular Telescope instruments MODS and LUCI2, and compared with a spectrum of similar spectral resolution and sensitivity level taken during quiescence. Together with the enhancement of the continuum, the outburst spectrum presents a definitely higher number of emission lines, in particular HI recombination lines of the Balmer, Paschen, and Brackett series, along with bright permitted lines of several species, forbidden atomic lines, and CO ro-vibrational lines. Both mass accretion and mass loss rates have significantly increased (by to about an order of magnitude, mass accretion rate = 1.2-4.8 10^-8 M_sun/yr, mass loss rate = 0.8-2 10^-9 M_sun/yr) with respect to the quiescence phase. If compared with previous outbursts, the present one appears less energetic. Alternatively, it could already be in the fading phase (with the maximum brightness level reached when the source was not visible), or, viceversa, still in the rising phase., Comment: Accepted ApJ Letters

We present an in-depth near-IR analysis of a sample of H 2 outflows from young embedded sources to compare the physical properties and cooling mechanisms of the different flows. The sample comprises 23 outflows driven by Class 0 and I sources having low-intermediate luminosity. We have obtained narrow band images in H 2 2.12 μ m and [$\ion{Fe}{ii}$] 1.64 μ m and spectroscopic observations in the range 1-2.5 μ m. From [$\ion{Fe}{ii}$] images we detected spots of ionized gas in ~74% of the outflows which in some cases indicate the presence of embedded HH-like objects. H 2 line ratios have been used to estimate the visual extinction and average temperature of the molecular gas. A v values range from ~2 to ~15 mag; average temperatures range between ~2000 and ~4000 K. In several knots, however, a stratification of temperatures is found with maximum values up to 5000 K. Such a stratification is more commonly observed in those knots which also show [$\ion{Fe}{ii}$] emission, while a thermalized gas at a single temperature is generally found in knots emitting only in molecular lines. Combining narrow band imaging (H 2 , 2.12 μ m and [$\ion{Fe}{ii}$], 1.64 μ m) with the parameters derived from the spectroscopic analysis, we are able to measure the total luminosity of the H 2 and [$\ion{Fe}{ii}$] shocked regions ($L_{\rm H_2}$ and $L_{[\ion{Fe}{ii}]}$) in each flow. H 2 is the major NIR coolant with an average $L_{\rm H_2}$/$L_{[\ion{Fe}{ii}]}$ ratio of ~10 2 . We find that ~83% of the sources have a $L_{\rm H_2}$/ L bol ratio ~0.04, irrespective of the Class of the driving source, while a smaller group of sources (mostly Class I) have $L_{\rm H_2}$/ L bol an order of magnitude smaller. Such a separation reveals the non-homogeneous behaviour of Class I, where sources with very different outflow activity can be found. This is consistent with other studies showing that among Class I one can find objects with different accretion properties, and it demonstrates that the H 2 power in the jet can be a powerful tool to identify the most active sources among the objects of this class.

We have performed a detailed study of the star-forming region associated with the IRAS source 08448-4343 in the cloud D of the Vela Molecular Ridge. Our investigation covers a wide spectral range from the near IR, through the thermal IR to the mm-band exploiting both imaging and spectroscopic facilities in each spectral regime. A picture emerges of a dust structure which hosts a near IR cluster and multiple well-collimated H2 jets; these jets originate from different sources lying in a compact region at the cluster centre. The peak of the 1.2 mm map does not coincide with the IRAS peak, thus tracing a less evolved and denser region with a colder dust with respect to that traced by IRAS. This view is also confirmed by the observations of CS transitions from J = 2− 1t oJ = 7−6. The mm peak can be associated with the position of a red object, already proposed in previous studies as the driving source of the main jet in the field. This jet, extended along more than 0.3 pc, is composed of individual knots whose radial velocities decrease with increasing distance from the central source, which is resolved into at least six 2 µm peaks. The reddest and coldest of these peaks is well aligned with the inner knots of the jet. The spectral energy distribution of the central source resembles that of an intermediate luminosity, Class I protostar, whose youth is discussed in terms of the efficiency of the energy transfer into the jet.

The REM Observatory, recently installed and commissioned at la Silla Observatory Chile, is the first moderate aperture robotic telescope able to cover simultaneously the visible-NIR (0.45-2.3 microns) wavelength range. Due to its very fast pointing and its full robotization REM is conceived for fast transients observation. The high throughput Infrared Camera (REMIR) and the Visible imaging spectrograph (ROSS), simultaneously fed by a dichroic, allow to collect high S/N data in an unprecedented large spectral range on a telescope of this size. The REMobservatory is an example of a versatile and agile facility necessary complement to large telescopes in fields in which rapid response and/or target pre-screening are necessary. This paper describes the principal Characteristics and operation modes of the REM observatory and gives on overview of the preliminary results obtained during the commissioning phase. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The star forming region associated with IRAS 08211-4158 and located in the Vela Molecular Ridge (VMR) has been investigated with low ( R≈ 600) and high resolution ( R≈ 9000) near infrared spectroscopy (1−2.5 µm) together with narrow band ((Fe  )a nd H 2) and broad band (H, K, L, M) imaging. The photometric results allow us to identify for the first time a young cluster with the less evolved star lying toward its center. Our results confirm that the most massive stars found in the clusters of the VMR do not form before the low mass ones. In particular, the only bipolar jet detected across the investigated field is driven by the most massive object which lacks an optical counterpart. Such a jet is composed of individual knots showing several H2 and (Fe ) emission lines indicative of a coexistence of different shocks responsible for their excitation. Physical parameters of the emitting gas such as electron density, extinction and temperature have been derived from the low resolution spectroscopy. Some knots are already thermalized, while other present a stratification of temperature up to values of 5000 K. Through high resolution spectroscopy the (Fe ) lines profile for the majority of the knots can be resolved in a double peaked structure which is consistent with bow shock model predictions. Moreover, the radial velocity component is determined for different knots. Finally, by comparing (Fe ) images taken in different epochs, we have been able to derive the proper motion for some knots, hence to evaluate their total velocity (∼300 km s −1 ), the dynamical age and the jet inclination with respect to the plane of the sky.

This paper discusses a model for the continuum emission of the Herbig Ae/Be stars in the light of an updated set of observational data spanning 5 orders of magnitude in wavelength and including the low-resolution spectra obtained with the Short Wavelength Spectrometer and Long Wavelength Spectrometer on board the Infrared Space Observatory (ISO). The model is used to reproduce the continuum emission of the 36 Herbig Ae/Be stars included in the list by The and coworkers and observed by ISO. The circumstellar matter responsible for the observed spectral energy distributions has been investigated by comparing the set of the observations with the model spectra computed for different possible distributions of circumstellar matter. Cases have been considered with the circumstellar regions partially evacuated along the polar axis by the action of the stellar wind, a phenomenon that is quite common in these pre-main-sequence objects. The inclusion of the polar cavities indirectly allows geometries in which a small-scale disklike structure around the central star is present. The possible coexistence of two different density profiles, in the inner and the outer region of the envelope, respectively, has been also considered. The comparison of the computed models with the observed spectral energy distributions selects the parameter values in such a way that the larger dust grains are preferentially associated with the later spectral types. We find that 17 objects are reasonably fitted, eight of which with a purely spherical model and the remaining nine with the inclusion of the polar cavities. For 10 further objects the fit is worse, and for the remaining nine, almost all associated to IR companions, our model is clearly inappropriate. A linear relationship is suggested between the logarithm of the initial density n0 and the exponent p of the power law n(r) = n0(R*/r)p adopted for the circumstellar density distribution.

We present the latest results from a sensitive (K ∼ 18 mag) near-infrared (JHK) imaging survey of IRAS selected young stellar objects associated with the Vela molecular ridge. These enlarge the sample of 12 fields, previously studied, adding 10 sites of recent star formation. The spectral energy distributions derived from near-infrared and 1.3-mm photometry allowed to identify at least 5 Class I sources. Their bolometric luminosities indicate that they are protostellar objects of intermediate mass (∼2-10 M� ). Herbig Ae/Be stars and compact UCHII regions could account for the far infrared emission towards some of the remaining fields. The most luminous IRAS sources have also been found associated with young embedded star clusters. The physical properties of the clusters have been determined and used to improve on the statistical relationships already suggested by our previous work. They have sizes of >0.1 pc and volume densities of 10 3 -10 4 stars pc −3 . Where identified, the Class I sources tend to lie near the centre of the clusters and it is confirmed that the most massive ones are associated with the richest clusters. The less luminous Class I sources (∼10 2 L� ) are found either isolated or within small groups of young stellar objects. It is proposed to use the relationship between the bolometric luminosity of the IRAS sources and the total number of cluster members as a test of the initial mass function at the highest masses.

As part of a 1-2.5m spectroscopic survey of jets and molecular outflows, we present the spectra of three Herbig Haro chains (HH111, HH240/241, HH120) characterized by strong emission from several Feii transitions originating from the first 13 fine structure levels. Such emission is correlated with optical Sii emission and appears to decrease moving away from the driving source. From the analysis of the Feii lines we have derived electron densities values in the range 3 10 3 - 2 10 4 cm 3 , which are systematically larger than those inferred from optical Sii line ratios. We suggest that Feii lines, having critical densities higher than the optical Sii transitions, trace either regions of the post-shock cooling layers with higher compression, or a section of the jet axis at a higher degree of ionization. Strong H2 emission lines are also detected along the three flows and their analysis indicates that a combination of dierent shocks can be responsible for their excitation in the dierent objects. Consequently the Feii line emission, which requires the presence of fast dissociative shocks, is completely independent from the excitation mechanism giving rise to the molecular emission. In addition to the Feii and H2 lines, emission from other species such as Ci ,S ii ,N i as well as recombination lines from the Paschen series are detected and have been used as a reference to infer the gas-phase iron abundance in the observed HH objects. We estimate a grain destruction eciency of about 30-60%: the highest value is found for HH240A, which also shows the highest degree of excitation among the observed objects.

The far-infrared spectra (45-197 μm) of 28 low-luminosity young embedded objects have been studied in order to search for possible evolutive trends in the observed spectral features. The low-resolution spectra from 45 to 197 μm of 17 Class 0 and 11 Class I sources taken with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory have been used for this analysis. The most prominent features presented by these spectra are the [O I] 63 and 145 μm fine-structure lines and pure rotational lines from the abundant molecules CO, H2O, and OH. Clear differences are found, however, between the spectra of the two classes of objects. Water lines, which are prominent in the spectra of Class 0 sources, are not observed in Class I objects, with an upper limit 10-5 on the H2O abundance. Furthermore, the total cooling due to molecular emission in Class 0 sources is on average significantly larger than in Class I sources, while the cooling due to atomic oxygen is fairly constant among the two classes of objects. Finally, the total gas cooling as traced by the far-infrared lines (LFIR) is correlated with the bolometric luminosity for the Class 0 sample of sources, with an LFIR/Lbol ratio (~10-2) of about an order of magnitude larger than in Class I sources. We suggest that most of the observed emission lines originate from shocks at the base and along the source outflows. In such a case these results can be interpreted in terms of a change in the modality of the interaction between the protostellar jet and the circumstellar environment. During the Class 0 phase the impact of energetic flows with the dense ambient medium gives rise to a strong component of nondissociative C-type shock, while during the Class I phase such impact produces less energetic shocks with an enhanced dissociative J-type component. Finally, the low H2O abundance found in Class I sources can be explained by the action of the progressively less shielded interstellar UV field.

Spectroscopy in the J band (even at low resolutions of R 103) is a mode commonly available in most near-IR spectrographs but is rarely exploited in star formation studies. We show how it is a crucial tool to tracing the physics (temperature, density, excitation mechanisms) of protostellar jets and Herbig-Haro (HH) objects. In this framework the spectrum of HH 43 is revisited as both a clear demonstration of our statement and a case of slow J-type shock excitation.

We present narrowband imaging in the 2.122 μm transition of H2 and in the 1.644 μm transition of [Fe II] of a sample of 12 protostellar candidates and three Herbig-Haro (HH) objects belonging to the Vela molecular ridge (VMR). Out of the 15 investigated fields, we detected H2 emission in IRS 63, 17, 19, 21, and 8 (according to our catalog), while [Fe II] was observed toward only one source (IRS 8), where a counterjet has been identified for the first time. H2 and [Fe II] images have been combined to trace the different shock conditions along this jet. In addition, a new pure molecular H2 jet was discovered in IRS 17, which results in about 20 knots of emission extending up to 0.3 pc from the central driving source. IR spectroscopy (1.55-2.55 μm) at a resolution of ≈600 of the most prominent knots has revealed a large number of H2 emission lines, which were used to evaluate both the extinction and the excitation temperature along the flow. The observed increase of the excitation temperature with the distance from the central source was interpreted as being due to a decrease of the flow velocity with time or, alternatively, to the fact that internal knots travel in a medium already put into motion by previous shock events. Comparisons with model predictions indicate nondissociative C-shocks as the most likely mechanism for line excitation. Finally, the presence of a common alignment of the detected flows with the Galactic plane indicates that the Galactic B field affects the star formation on large scales in VMR.

We report 3-5 μ m IR spectroscopy obtained with VLT-ISAAC on the IRS17 molecular hydrogen jet in the Vela-D Molecular Cloud. Together with H 2 emission lines from the $v =$ 1 rovibrational state, the spectra show several pure rotational lines of the fundamental state with excitation temperature up to ~22 000 K. We show how theoretical rotation diagrams indicate these lines as unique both to probe the presence of collisionally excited gas in NLTE conditions and to infer the gas density.

The ISO-SWS full grating spectrum (2.3-45 μ m) of the Herbig Be star MWC 297 is presented. The spectrum is dominated by a strong continuum with superimposed emission lines and features both in absorption and in emission. In particular, we detect in emission 23 Hi recombination lines of the Brackett, Pfund and Humphreys series and four PAH features, while in absorption two broad silicate bands at 9.7 and 16.4 μ m, solid CO 2 at 4.27 μ m and solid H 2 O at 2.96 μ m have been observed. The ISO-SWS spectrum has been combined with ISO-LWS data and ground based photometry to derive the spectral energy distribution (SED) from optical to radio wavelengths. The observed SED has been fitted with a model that assumes a spherical dusty envelope parametrized by density and temperature power laws, deriving suitable values for the spectral type (B2), the visual extinction (7.5 mag) and the distance (280 pc). Consistent determination of the extinction and estimates of both the source mass loss rate ($9\times 10^{-7} M_{\odot}$ yr -1 ) and the size of the emitting ionized region (30 stellar radii) have been derived by the analysis of the Hi recombination lines of the Brackett, Pfund and Humphreys series observed by ISO-SWS together with Paschen and Brackett lines observed from the ground. Some peculiarities have been observed in the ISO-SWS spectrum of this source: i ) the ratio between the column density of the solid $\rm CO_2$ and $\rm H_2O$ ($2.0\pm 1.5$) higher than the values usually observed and ii ) the presence of a silicate broad absorption band at 16.4 μ m stronger than the 9.7 μ m absorption. The observed silicate absorption features are probably due to the extended dusty cloud in which the star is embedded and their relative strengths could be evidence that they are composed by processed grains.

We present near infrared images of the bright rimmed globule IC 1396-N in the H2 2.12 m narrow band lter as well as in broad band J, H and K lters. We detected several chains of collimated H2 knots inside the globule, having dierent luminosities but similar orientations in the sky. Most of the knots are associated with peaks of high velocity CO emission, indicating that they trace shocked regions along collimated stellar jets. From the H2 knots morphology and orientation, we identify at least three dierent jets: one of them is driven by the young protostar associated with IRAS 21391+5802, which represents the most luminous object in the region, while we were able to identify only one of the two other driving sources by means of near infrared photometry. Our photometry reveals the existence of a cluster of young embedded sources located in a south-north line which follows the distribution of the high density gas and testies for a highly ecient star formation activity through all the globule.

We have investigated with the Long Wavelength Spectrometer (LWS) of the Infrared Space Observatory (ISO) the far-infrared spectra (43-197 μm) of a sample of 17 class 0 sources and their associated outflows. In addition to [O I] 63 μm, the pure rotational lines of abundant molecules such as CO, H2O, and OH are frequently observed in these sources, at variance with more evolved young stellar objects. We found, in agreement with previous studies conducted on individual sources, that the molecular line excitation arises from small regions, with typical sizes of 10-9 sr, of warm (200 < T < 2000 K) and dense gas (104 < n < 107 cm-3), compressed after the passage of shocks. In particular, we found slow, nondissociative shocks as the main mechanism at the origin of the molecular gas heating, while the bulk of the [O I] 63 μm line emission is due to the dissociative J-shock component arising from the Mach disk at the head of the protostellar jet, as testified by the fact that this line emission happens to be a good tracer of the source mass-loss rate. Large abundances of gas-phase H2O are commonly estimated, with values that appear to be correlated with the gas temperature. The total far-infrared (FIR) line cooling LFIR = L(O ) + L(CO) + L(H2O) + L(OH), which amounts to ~10-2 to 10-1 L☉, is roughly equal to the outflow kinetic luminosity as estimated by means of millimeter molecular mapping. This circumstance demonstrates that the FIR line cooling can be a valid direct measure of the power deposited in the outflow, not affected by geometrical or opacity problems like the determination of Lkin or by extinction problems like the near-infrared shocked H2 emission. We finally remark that the strong molecular emission observed, and in particular H2O emission, is a peculiarity of the environments of class 0 sources. The present analysis shows that the ratio between FIR molecular line luminosity and bolometric luminosity (Lmol/Lbol) is always larger than ~10-3 in class 0 objects. We suggest that this parameter could be used as a further criterion for identifying future class 0 candidates.

We have used the two spectrometers on the Infrared Space Observatory to observe the HH 7¨11 —ow, its redshifted counterpart, and the candidate exciting source SVS 13 in the star formation region NGC 1333. We detect atomic ((O I )6 3km, (O I) 145 km, (Si II) 34.8 km, (C II) 158 km) and molecular (H 2 , CO, lines at various positions along the bipolar —ow. Most of the observed lines can be explained H 2 O) in terms of shock-excited emission. In particular, our analysis shows that dissociative (J-type) and non- dissociative (C-type) shocks are simultaneously present everywhere along both lobes of the —ow. We con—rm the low-excitation nature of the Herbig-Haro nebulosities, with shock velocities km v s ( 40¨50 s~1. Toward both lobes of the out—ow, we —nd preshock densities of cm~3 for both the J and n 0 D 104 C components, implying kG for In the central region of the —ow, close to the excit- B 0 D 100 B 0 P n 0. ing source, the preshock density deduced for the C-shock component is cm~3, suggesting a n 0 D 105 magnetic —eld D3 times stronger. We propose that the de—ciency of gas-phase water in the postC-shock regions is caused by freezing onto warm grains processed through the J-shock front and traveling along the magnetic —eld lines. The total observed cooling from the dissociative shock components is consistent with the power lost by a slow molecular out—ow accelerated by a fast neutral HI wind. Finally, the skin of the cloud seen in projection toward the —ow appears to be weakly photoionized by BD )30i549, the dominant illuminating source of the NGC 1333 re—ection nebula. Subject headings: ISM: Herbig-Haro objectsISM: individual (HH 7¨11) ¨ ISM: lines and bands ¨ ISM: moleculesstars: formation

We present the rst results of a sensitive (K 17 mag) near IR (JHK) imaging survey of a complete IRAS selected sample of Young Stellar Objects (YSO's) belonging to a Giant Molecular Cloud (GMC) located in the Vela Molecular Ridge (VMR). We provide accurate po- sition and photometry for more than 1300 sources, along with the identication of possible NIR counterparts of the IRAS objects. Through near infrared and 1.3 mm photom- etry we have determined the spectral energy distributions of 11 newly discovered Class I sources and possibly one Herbig Ae/Be star. Their bolometric luminosities indicate that they are protostellar objects of intermediate masses ( 10M) with envelopes containing a not negligible frac- tion of the central condensed matter. Many sources are as- sociated to diuse emission which hosts multiple systems of point-like objects. Although clustering is well evident, the NIR counterparts of the IRAS sources seem to be sin- gle objects and quite often there are more than one source in the eld with JHK colours typical of Class I objects. These ndings support the fact that in VMR, as well, stars of dierent masses are sharing the same birthplace.

Dense atomic jets from young stars copiously emit in [FeII] IR lines, which can, therefore, be used to trace the immediate environments of embedded protostars. We want to investigate the morphology of the bright [FeII] 1.64um line in the jet of the source HH34 IRS and compare it with the most commonly used optical tracer [SII]. We analyse a 1.64um narrow-band filter image obtained with the Large Binocular Telescope (LBT) LUCI instrument, which covers the HH34 jet and counterjet. A Point Spread Function (PSF) deconvolution algorithm was applied to enhance spatial resolution and make the IR image directly comparable to a [SII] HST image of the same source. The [FeII] emission is detected from both the jet, the (weak) counter-jet, and from the HH34-S and HH34-N bow shocks. The deconvolved image allows us to resolve jet knots close to about 1\arcsec from the central source. The morphology of the [FeII] emission is remarkably similar to that of the [SII] emission, and the relative positions of [FeII] and [SII] peaks are shifted according to proper motion measurements, which were previously derived from HST images. An analysis of the [FeII]/[SII] emission ratio shows that Fe gas abundance is much lower than the solar value with up to 90% of Fe depletion in the inner jet knots. This confirms previous findings on dusty jets, where shocks are not efficient enough to remove refractory species from grains., Comment: 5 pages, 4 figures, note accepted by A&A

We present the results of our project for the design and construction and on-sky test of silicon grisms. The fabrication of such devices is a complex and critical process involving litho-masking, anisotropic etching and direct bonding techniques. After the successful fabrication of the silicon grating, we have optimized the bonding of the grating onto the hypotenuse of a silicon prism to get the final prototype. After some critical phases during the experimentation a silicon grism with 363 grooves/mm and a blaze angle of 14 degrees has been eventually fabricated. The application of an A/R coating on both the surfaces has been the last step: this procedure is critical because of the groove geometry of the diffraction grating, whose performace might be compromised by the coating. Then, the grism was inserted in the filter wheel of the Near Infrared camera NICS, at the focal plane of the National Galileo Telescope (TNG), the 3.5 m Italian facility in the Canary Islands (E). The result of the on-sky tests are given in detail., Comment: 9 pages, 13 figures, 1 table. Presented at SPIE Astronomical Telescope + Instrumentation 2014 (Ground-based and Airbone Instrumentation for Astronomy, 9151-203). To be published in Proceeding of SPIE Volume 9151

Flux variability is a common feature of Young Stellar Objects (YSOs), which is often related to intermittent events of disk accretion (EXors events in case of 3–4 magnitudes variations). Recently, thanks to the surveys carried out by the space missions Spitzer and WISE, it has become possible to perform statistical studies on the mid-IR variability on large samples of YSOs. As a follow-up of our recent statistical study on five star forming regions (Antoniucci et al., Astrophys. J. 782:51, 2014), we present the 3–5 µm variability study of the YSOs population of the Vela-D star forming region. We have compared the 3.6 µm and 4.5 µm Spitzer-IRAC fluxes of 181 YSOs in Vela-D with their WISE fluxes at 3.4 µm and 4.6 µm and selected those objects simultaneously varying in both bands. We have iden- tified a robust sample of 34 variables. On the base of the in- frared excess of the Spectral Energy Distribution (SED) and the magnitude vs. color variations, we select 5 EXors can- didates, which will be systematically monitored to firmly ascertain their nature. The selected 34 variables represent ∼18 % of the YSOs detected with Spitzer and WISE, a per- centage higher than that of other young star forming regions. Conversely, the percentage of candidate EXors (2.7 %) is quite similar to that measured in Perseus, Ophiuchus and Serpens, and also equals that found in Vela-D on the base of Spitzer variability (Giannini et al., Astrophys. J. 704:606, 2009). Consistently with our finding presented in Antoni- ucci et al. (2014), this fraction equals the probability of ob- serving the source once in burst and once in quiescence, un- der the hypothesis that the time elapsed between the two events is of about 0.5–1 year. Of the 5 selected EXors candi- dates, 3 are Class I sources, and 2 are flat-spectrum sources, a circumstance that suggests that accretion-driven variabil- ity is a common phenomenon during the earlier phases of the protostellar evolution. In the light of the new WISE data, we also re-examine a sample of 10 variables, which we had already selected in Giannini et al. (2009). From the inspec- tion of their light curves, we select two flat-spectrum sources as the best EXors candidates.

We present a collection of WISE photometry of EXor sources and candidates (more recently identified). This represents the first complete survey of such objects in the mid-IR (3.4 - 22 um) that was carried out with the same instrumentation. Two-color diagrams constructed with WISE data evidence a clear segregation between classical and newly identified sources, being these latter characterized by colder (and less evolved) circumstellar disks. By combining 2MASS and WISE data, we obtain spectral energy distributions (SED's) that are compatible with the existence of an inner hole in the circumstellar disk. A compilation of all EXor observations given in the literature at wavelengths very similar to those of WISE is also provided. This allows us to study their mid-IR variability, which has been poorly investigated so far and without any coordination with shorter wavelengths surveys. The presented it WISE photometry and the compilation of the literature data are intended as a first step toward the construction of a significant database in this spectral regime. Preliminary indications on the mechanisms responsible for the luminosity fluctuations are provided., Accepted by New Astronomy

We present the results of a comparison between classical and newly identified EXor based on literature data and aimed at recognizing possible differences or similarities of both categories. Optical and near-IR two-color diagrams, modalities of fluctuations, and derived values of the mass accretion rates are indicative of strong similarities between the two samples. We demonstrate how the difference between the outburst and the quiescence spectral energy distribution of all the EXor can be well fitted with a single blackbody, as if an additional thermal component appears during the outbursting phase. Temperatures of this additional component span between 1000 and 4500 K, while the radii of the emitting regions (assumed to be a uniform disk) span between 0.01 and 0.1 AU, sizes typical of the inner portions of the circumstellar disk. Spots persisting up to 50% of the outburst duration, not exceeding the 10% of the stellar surface, and with temperatures compatible with the EXor mass accretion rates, are able to account for both the appearance of the additional thermal component and the dust sublimation in the inner structures of the disk. We also compare the EXor events with the most significant color and magnitude fluctuations of active T Tauri stars finding that (i} burst accretion phenomena should also be important for this latter class; (ii} EXor events could be more frequent then those accidentally discovered. Remarkable is the case of the source V2493 Cyg, a T Tauri star recently identified as a strong outbursting object: new optical and near-IR photometric and spectroscopic data are presented trying to clarify its EXor or FUor nature., Accepted for publication in ApJ

We present a 3-mm and 1.3-cm spectral line survey conducted with the Mopra 22-m and Parkes 64-m radio telescopes of a sample of 40 cold dust cores, previously observed with BLAST, including both starless and proto-stellar sources. 20 objects were also mapped using molecular tracers of dense gas. To trace the dense gas we used the molecular species NH3, N2H+, HNC, HCO+, H13CO+, HCN and H13CN, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes. The selected cores have a wide variety of morphological types and also show physical and chemical variations, which may be associated to different evolutionary phases. We find evidence of systematic motions in both starless and proto-stellar cores and we detect line wings in many of the proto-stellar cores. Our observations probe linear distances in the sources >~0.1pc, and are thus sensitive mainly to molecular gas in the envelope of the cores. In this region we do find that, for example, the radial profile of the N2H+(1-0) emission falls off more quickly than that of C-bearing molecules such as HNC(1-0), HCO+(1-0) and HCN(1-0). We also analyze the correlation between several physical and chemical parameters and the dynamics of the cores. Depending on the assumptions made to estimate the virial mass, we find that many starless cores have masses below the self-gravitating threshold, whereas most of the proto-stellar cores have masses which are near or above the self-gravitating critical value. An analysis of the median properties of the starless and proto-stellar cores suggests that the transition from the pre- to the proto-stellar phase is relatively fast, leaving the core envelopes with almost unchanged physical parameters., Submitted for publication to Astronomy & Astrophysics on January 18th, 2012

MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared Spectrograph for the Very Large Telescope (VLT), selected by ESO for a Phase A study. The baseline design consists of 1000 fibers deployable over a field of view of 500 square arcmin, the largest patrol field offered by the Nasmyth focus at the VLT. The total wavelength coverage is 0.8um-1.8um and two resolution modes: medium resolution and high resolution. In the medium resolution mode (R=4,000-6,000) the entire wavelength range 0.8um-1.8um is observed simultaneously, while the high resolution mode covers simultaneously three selected spectral regions: one around the CaII triplet (at R=8,000) to measure radial velocities, and two regions at R=20,000 one in the J-band and one in the H-band, for detailed measurements of chemical abundances. The grasp of the 8.2m Very Large Telescope (VLT) combined with the large multiplex and wavelength coverage of MOONS - extending into the near-IR - will provide the observational power necessary to study galaxy formation and evolution over the entire history of the Universe, from our Milky Way, through the redshift desert and up to the epoch of re-ionization at z>8-9. At the same time, the high spectral resolution mode will allow astronomers to study chemical abundances of stars in our Galaxy, in particular in the highly obscured regions of the Bulge, and provide the necessary follow-up of the Gaia mission. Such characteristics and versatility make MOONS the long-awaited workhorse near-IR MOS for the VLT, which will perfectly complement optical spectroscopy performed by FLAMES and VIMOS., 9 pages, 5 figures. To appear in the proceedings of the SPIE Astronomical Instrumentation + Telescopes conference, Amsterdam, 2012

We report the results of a simulation and reconstruction of observations of a young stellar object (YSO) jet with the LINC-NIRVANA (LN) interferometric instrument, which will be mounted on the Large Binocular Telescope (LBT). This simulation has been performed in order to investigate the ability of observing the weak diffuse jet line emission against the strong IR stellar continuum through narrow band images in the H and K atmospheric windows. In general, this simulation provides clues on the image quality that could be achieved in observations with a high dynamic range. In these cases, standard deconvolution methods, such as Richardson-Lucy, do not provide satisfactory results: we therefore propose here a new method of image reconstruction. It consists in considering the image to be reconstructed as the sum of two terms: one corresponding to the star (whose position is assumed to be known) and the other to the jet. A regularization term is introduced for this second component and the reconstruction is obtained with an iterative method alternating between the two components. An analysis of the results shows that the image quality obtainable with this method is significantly improved with respect to standard deconvolution methods, reducing the number of artifacts and allowing us to reconstruct the original jet intensity distribution with an error smaller than 10%., Comment: From the proceedings of the SPIE 2012 conference, 11 pages, 7 figures

Characterising stellar and circumstellar properties of embedded young stellar objects (YSOs) is mandatory for understanding the early stages of the stellar evolution. This task requires the combination of both spectroscopy and photometry, covering the widest possible wavelength range, to disentangle the various protostellar components and activities. As part of the POISSON project, we present a multi-wavelength spectroscopic and photometric investigation of embedded YSOs in L1641, aimed to derive the stellar parameters and evolutionary stages and to infer their accretion properties. Our database includes low-resolution optical-IR spectra from the NTT and Spitzer (0.6-40 um) and photometric data covering a spectral range from 0.4 to 1100 um, which allow us to construct the YSOs spectral energy distributions (SEDs) and to infer the main stellar parameters. The SED analysis allows us to group our 27 YSOs into nine Class I, eleven Flat, and seven Class II objects. However, on the basis of the derived stellar properties, only six Class I YSOs have an age of ~10^5 yr, while the others are older 5x10^5-10^6 yr), and, among the Flat sources, three out of eleven are more evolved objects (5x10^6-10^7 yr), indicating that geometrical effects can significantly modify the SED shapes. Inferred mass accretion rates (Macc) show a wide range of values (3.6x10^-9 to 1.2x10^-5 M_sun yr^-1), which reflects the age spread observed in our sample. Average values of mass accretion rates, extinction, and spectral indices decrease with the YSO class. The youngest YSOs have the highest Macc, whereas the oldest YSOs do not show any detectable jet activity in either images and spectra. We also observe a clear correlation among the YSO Macc, M*, and age, consistent with mass accretion evolution in viscous disc models., Comment: 61 pages, 16 figures; A&A in press

We present the results of the analysis of LR optical-NIR spectra (0.6-2.4 um) of a sample 47 YSOs in the ChaI and II star-forming clouds. These data are part of the POISSON project (Protostellar Optical-Infrared Spectral Survey on NTT). The aim is to determine the accretion luminosity (Lacc) and mass accretion rate (Macc) of the sources through the analysis of the detected emission features. We also aim at verifying the reliability and consistency of the existing empirical relationships connecting emission line luminosity and Lacc. We employ five tracers (OI-6300A, Ha, CaII-8542A, Pab, and Brg) to derive the accretion luminosity. The tracers provide Lacc values showing different scatters when plotted as a function of L*. The Brg seems to be the most reliable, because it gives the minimum Lacc dispersion over the entire range of L*, whereas the other tracers provide much more scattered Lacc values, which are not expected for our homogeneous sample. The comparison between Lacc(Brg) and Lacc obtained from the other tracers also shows systematic differences among the empirical relationships. These may probably be ascribed to different excitation mechanisms contributing to the line emission, which may vary between our sample and those where the relationships were calibrated. Adopting the Lacc derived from Brg, we find Lacc=0.1L*-1L* for all sources, and Macc of the order of 10^-7-10^-9 Msun/yr. The Macc derived in ChaI are proportional to M*^2, as found in other low-mass star-forming regions. The discrepancies observed in the case of Lacc(Brg) and Lacc(Pab) can be related to different intrinsic Pab/Brg, ratios. The derived ratios show the existence of two different emission modalities, one that agrees with predictions of both wind and accretion models, the other suggesting optically thick emission from relatively small regions (10^21-10^22 cm^-3) with gas at low temperatures (, 22 pages, 8 figures, accepted for publication in A&A; institute affiliations and typos corrected

The Vela-D region, according to the nomenclature given by Murphy & May (1991), of the star forming complex known as the Vela Molecular Ridge (VMR), has been recently analyzed in details by Olmi et al. (2009), who studied the physical properties of 141 pre- and proto-stellar cold dust cores, detected by the ``Balloon-borne Large-Aperture Submillimeter Telescope'' (BLAST) during a much larger (55 sq. degree) Galactic Plane survey encompassing the whole VMR. This survey's primary goal was to identify the coldest, dense dust cores possibly associated with the earliest phases of star formation. In this work, the dynamical state of the Vela-D cores is analyzed. Comparison to dynamical masses of a sub-sample of the Vela-D cores estimated from the 13CO survey of Elia et al. (2007), is complicated by the fact that the 13CO linewidths are likely to trace the lower density intercore material, in addition to the dense gas associated with the compact cores observed by BLAST. In fact, the total internal pressure of these cores, if estimated using the 13CO linewidths, appears to be higher than the cloud ambient pressure. If this were the case, then self-gravity and surface pressure would be insufficient to bind these cores and an additional source of external confinement (e.g., magnetic field pressure) would be required. However, if one attempts to scale down the 13CO linewidths, according to the observations of high-density tracers in a small sample of sources, then most proto-stellar cores would result effectively gravitationally bound., This paper has 12 pages and 6 figures. Accepted for publication by the Astrophysical Journal on July 19, 2010

The current observational scenario pertaining to the study of low-mass star formation is discussed together with the evolutionary sequence that such a scenario seems to suggest. The opportunities offered by the spectrometers on board of the ISO satellite for improving our understanding of the involved physical processes are then discussed.

The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis when associated to the PRIMA dual-beam facility. The concept of VSI consists on 6 sub-systems: a common path distributing the light between the fringe tracker and the scientific instrument, the fringe tracker ensuring the co-phasing of the array, the scientific instrument delivering the interferometric observables and a calibration tool providing sources for internal alignment and interferometric calibrations. The two remaining sub-systems are the control system and the observation support software dedicated to the reduction of the interferometric data. This paper presents the global concept of VSI science path including the common path, the scientific instrument and the calibration tool. The scientific combination using a set of integrated optics multi-way beam combiners to provide high-stability visibility and closure phase measurements are also described. Finally we will address the performance budget of the global VSI instrument. The fringe tracker and scientific spectrograph will be shortly described.

We present the optical and cryo-mechanical solutions for the Spectrograph of VSI (VLTI Spectro-Imager), the second generation near-infrared (J, H and K bands) interferometric instrument for the VLTI. The peculiarity of this spectrograph is represented by the Integrated Optics (IO) beam-combiner, a small and delicate component which is located inside the cryostat and makes VSI capable to coherently combine 4, 6 or even 8 telescopes. The optics have been specifically designed to match the IO combiner output with the IR detector still preserving the needed spatial and spectral sampling, as well as the required fringe spacing. A compact device that allows us to interchange spectral resolutions (from R=200 to R=12000), is also presented., 12 pages, 11 figures, SPIE Conference - Marseille 2008

LINC-NIRVANA (LN) is a Fizeau interferometer that will provide for the “rst time coherent images in the near-IR combining the beams from the two Large Binocular Telescope (LBT)arms, by adopting a Multi-ConiugateAdaptive Optics system (MCAO) that allows for atmos pheric turbulence compensation. We applied a softwarefor the simulation and the reconstruction of LN images (AIRY-LN, see Desider´ aetal. 1 this Conference) in twospeci“c scienti“c cases: a relatively distant galaxy at redshift about 1 and a collimated jet from a Young StellarObject (YSO). These two cases have been chosen to test the capability of LN in the observations of faint andsmall (1-2 arcsec) extragalactic objects and objects with diu se emission and high dynamical range, respectively.A total of six images at dieren t hour angles have been obtained for both cases. Using these simulated images, weobtained the “nal reconstructed images using the software package AIRY-LN. These images have been analyzedwith the standard data reduction software (IRAF and IDL). Our analysis show that the reconstruction algorithmis fundamental to obtain a good reproduction of the original ”ux and morphology while the optimal number ofiterations strongly depends on the scienti“c goal.Keywords: Image simulations, galaxies, young stellar objects

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13 will be imaged without requiring a brighter nearby reference object. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution enables a scientific program which serves a broad user community and at the same time provides the opportunity for breakthroughs in many areas of astrophysic including: probing the initial conditions for planet formation in the AU-scale environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities using technologies which have been extensively tested in the past and VSI requires little in terms of new infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the measurement of up to 28 visibilities in every wavelength channel within a few minutes. The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return., 12 pages, to be published in Proc. SPIE conference 7013 "Optical and Infrared Interferometry", Schoeller, Danchi, and Delplancke, F. (eds.). See also http://vsi.obs.ujf-grenoble.fr

Context. V1184 Tau is a young variable that for a long time has been monitored at optical wavelengths. Its variability has been ascribed to a sudden and repetitive increase of the circumstellar extinction (UXor-type variable), but the physical origin of this kind of variation, although hypothesized, has not been fully supported on an observational basis. Aims: With the aim of getting a new insight into the variability of V1184 Tau, we present here new photometric and spectroscopic observations that were taken in the period 2008-2015. During that time, the source reached the same high brightness level that it had before the remarkable fading of about 5 mag, which happened in 2004. The optical spectrum is the first to be obtained when the continuum was at its maximum level. Methods: All the observational data are interpreted in the framework of extinction-driven variability. In particular, we analyze light curves, optical and near-infrared colors, spectral energy distribution, and optical spectrum. Results: The emerging picture indicates that the source fading is due to an extinction increase of ∆AV ~ 5 mag, which is associated with the appearance of a strong infrared excess, attributable to a thermal component a T ~ 1000 K. From the flux of Hα, we derive a mass accretion rate in the range 10-11-5 × 10-10M☉ yr-1 s, which is marginally consistent with what is expected for a classical T Tauri star of similar mass. The source spectral energy distribution was fitted for both the high- and low- level of brightness. Remarkably, a scenario that is consistent with the known stellar properties (such as spectral type, mass, and radius) is obtained only if the distance to the source is of few hundreds of parsecs, in contrast with the commonly assumed value of ~1.5 kpc. Conclusions: Our analysis partially supports a previous model, according to which the circumstellar disk undergoes a periodic puffing, the observational effects of which both shield the central star and provide evidence of disk wind activity. However, since the mass accretion rate remains almost constant with time, the source is likely not subject to accretion bursts.

The Vela Molecular Ridge is one of the nearest intermediate-mass star forming regions, located within the galactic plane and outside the solar circle. Cloud D, in particular, hosts a number of small embedded young clusters. We present the results of a large-scale map in the dust continuum at 1.2 mm of a ~ 1deg x 1deg area within cloud D. The main aim of the observations was to obtain a complete census of cluster-forming cores and isolated (both high- and low-mass) young stellar objects in early evolutionary phases. The bolometer array SIMBA at SEST was used to map the dust emission in the region with a typical sensitivity of ~ 20 mJy/beam. This allows a mass sensitivity of ~ 0.2 Msun. The resolution is 24 arcsec, corresponding to ~ 0.08 pc, roughly the radius of a typical young embedded cluster in the region. The continuum map is also compared to a large scale map of CO(1-0) integrated emission. Using the CLUMPFIND algorithm, a robust sample of 29 cores has been obtained, spanning the size range 0.03 - 0.25 pc and the mass range 0.4 - 88 Msun. The most massive cores are associated both with red IRAS sources and with embedded young clusters, and coincide with CO(1-0) integrated emission peaks. The cores are distributed according to a mass spectrum ~ M^{-alpha} and a mass-versus-size relation ~ D^{x}, with alpha ~ 1.45 - 1.9 and x ~ 1.1 - 1.7. They appear to originate in the fragmentation of gas filaments seen in CO(1-0) emission and their formation is probably induced by expanding shells of gas. The core mass spectrum is flatter than the Initial Mass Function of the associated clusters in the same mass range, suggesting further fragmentation within the most massive cores. A threshold A_V ~ 12 mag seems to be required for the onset of star formation in the gas., 13 pages, 11 figures, to be published in Astronomy and Astrophysics

A new, unbiased Spitzer-MIPS imaging survey (~1.8 square degs) of the young stellar content of the Vela Molecular Cloud-D is presented. The survey is complete down to 5mJy and 250mJy at 24micron (mu) and 70mu, respectively. 849 sources are detected at 24mu and 52 of them also have a 70mu counterpart. The VMR-D region is one that we have already partially mapped in dust and gas millimeter emission, and we discuss the correlation between the Spitzer compact sources and the mm contours. About half of the 24mu sources are located inside the region delimited by the 12CO(1-0) contours (corresponding to only one third of the full area mapped with MIPS) with a consequent density increase of about 100% of the 24mu sources [four times for 70mu ones] moving from outside to inside the CO contours. About 400 sources have a 2MASS counterpart. So we have constructed a Ks vs. Ks-[24] diagram and identified the protostellar population. We find an excess of Class I sources in VMR-D in comparison with other star forming regions. This result is reasonably biased by the sensitivity limits, or, alternatively, may reflect a very short lifetime (, 29 pages, 14 figures. To appear in Ap.J

We investigate the relationship between the IR observed properties of the EXor variables and the mechanisms active during their evolutionary stage. To this aim, we have constructed a catalog of all the IR (1-100 micron) photometric and spectroscopic observations appearing during the last 30 years in the literature. New results of our monitoring program based on near- and mid-IR photometry and near-IR spectroscopy and polarimetry of one object (V1118 Ori) are presented, complementing those given in a previous paper and related to a different activity period. Our catalog indicates how the database accumulated so far is inadequate for any statistical study of the EXor events. Nevertheless, all the observational evidence can be interpreted into a coherent scheme. The sources that present the largest brightness variations tend to become bluer while brightening. The scenario of disk accretion based on viscous friction between particles agrees with the observations. The new results on V1118 Ori confirm such a general view. The striking novelty is represented by a near-IR spectrum of V1118 Ori taken 1 yr after the last monitored outburst: any emission line previously detected has now totally disappeared at our sensitivity. For the same source, mid-IR photometry is provided here for the first time and allows us to construct a meaningful SED. The first polarimetric data show that V1118 Ori is intrinsically polarized and its spotted, magnetized surface becomes recognizable during the less active phases., Comment: 23 pages. To be published to Astrophysical Journal

We present a NIR analysis of a sample of H2 outflows from young embedded sources to compare the physical properties and cooling mechanisms of the different flows. The sample comprises 23 outflows driven by Class 0 and I sources having low-intermediate luminosity. We have obtained narrow band images in H2 2.12um and FeII 1.64um and spectroscopic observations in the range 1-2.5um. H2 line ratios have been used to estimate the visual extinction and average temperature of the molecular gas. Av values range from 2 to 15mag; average temperatures range between 2000 and 4000K. In several knots a stratification of temperatures is found with maximum values up to 5000K. Such a stratification is more commonly observed in those knots which also show FeII emission, while a thermalized gas at a single temperature is generally found in knots emitting only in molecular lines. Combining narrow band imaging with the parameters derived from the spectral analysis, we are able to measure the total luminosity of the H2 and FeII shocked regions in each flow. H2 is the major IR coolant with an average L(H2)/L(FeII) ratio of 10^{-2}. 83% of the sources have a L(H2)/L(bol) ratio of 0.04, irrespective of the Class of the driving source, while a smaller group of sources have L(H2)/L(bol) an order of magnitude smaller.Such a separation reveals the non-homogeneous behaviour of ClassI, where sources with very different outflow activity can be found. This is consistent with other studies showing that among ClassI one can find objects with different accretion properties and it demonstrates that the H2 power in the jet can be a powerful tool to identify the most active sources of this class., Comment: 35 pages, 19 figures. To be published in Astronomy and Astrophysics

Near IR spectra obtained with ISAAC at VLT, have been used to pose constraints on the evolutionary state and accretion properties of a sample of five embedded YSOs located in the R CrA core. This sample includes three Class I sources (HH100 IR, IRS2 and IRS5), and two sources with NIR excesses (IRS6 and IRS3). Absorption lines have been detected in the medium resolution spectra of all the observed targets, together with emission lines likely originating in the disk-star-wind connected regions. We derived spectral types, veiling and stellar luminosity of the five observed sources, which in turn have been used to infer their mass and age adopting pre-main sequence evolutionary tracks. We find that in HH100 IR and IRS2 most of the bolometric luminosity is due to accretion, while the other three investigated sources, including the Class I object IRS5a, present a low accretion activity (L_{acc}/L_{bol} < 0.2). We observe a general correlation between the accretion luminosity, the IR veiling and the emission line activity of the sources. A correlation between the accretion activity and the spectral energy distribution slope is recognizable but with the notable exception of IRS5a. Our analysis therefore shows how the definition of the evolutionary stage of deeply embedded YSOs by means of IR colors needs to be more carefully refined., 17 pages, 13 figures, accepted on A&A

We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D, a star-forming region observed by both the Spitzer/NASA and Herschel/ESA space telescopes. The point-source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellar objects (YSOs), also including sources detected in less than four IRAC bands. Bona fide YSOs are selected by using appropriate color-color and color-magnitude criteria aimed at excluding both Galactic and extragalactic contaminants. The derived star formation rate and efficiency are compared with the same quantities characterizing other star-forming clouds. Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometric luminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel. The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects with bolometric temperatures below 70 K and luminosities of the order of the solar luminosity. Far-IR observations from the Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to obtain a band-merged photometric catalog of Herschel sources intended to independently search for protostars. We find 122 Herschel cores located on the molecular cloud, 30 of which are protostellar and 92 of which are starless. The global protostellar luminosity function is obtained by merging the Spitzer and Herschel protostars. Considering that 10 protostars are found in both the Spitzer and Herschel lists, it follows that in the investigated region we find 53 protostars and that the Spitzer-selected protostars account for approximately two-thirds of the total.

Aims. We report on the ongoing outburst of the young variable V1180 Cas, which is known to display characteristics in common with EXor eruptive variables. We present results that support the scenario of an accretion-driven nature of the brightness variations of the object and provide the first evidence of jet structures around the source. Methods. We monitored the recent flux variations of the target in the RC, J, H ,a ndK bands. New optical and near-IR spectra taken during the current high state of V1180 Cas are presented, in conjunction with H2 narrow-band imaging of the source. Results. Observed near-IR colour variations are analogous to those observed in EXors and consistent with excess emission originating from an accretion event. The spectra show numerous emission lines, which indicates accretion, ejection of matter, and an active disc.