- ID:
- ivo://CDS.VizieR/J/A+A/657/A129
- Title:
- 13 young brown dwarfs SINFONI spectra
- Short Name:
- J/A+A/657/A129
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Studies of the low-mass population statistics in young clusters are the foundation for our understanding of the formation of low-mass stars and brown dwarfs. Robust low-mass populations can be obtained through near-infrared spectroscopy, which provides confirmation of the cool and young nature of member candidates. However, the spectroscopic analysis of these objects is often not performed in a uniform manner, and the assessment of youth generally relies on the visual inspection of youth features whose behavior is not well understood. We aim at building a method that efficiently identifies young low-mass stars and brown dwarfs from low-resolution near-infrared spectra, by studying gravity-sensitive features and their evolution with age. We built a dataset composed of all publicly available (~2800) near-infrared spectra of dwarfs with spectral types between M0 and L3. First, we investigate methods for the derivation of the spectral type and extinction using comparison to spectral templates, and various spectral indices. Then, we examine gravity-sensitive spectral indices and apply machine learning methods, in order to efficiently separate young (<~10Myr) objects from the field. Using a set of six spectral indices for spectral typing, including two newly defined ones (TLI-J and TLI-K), we are able to achieve a precision below 1 spectral subtype across the entire spectral type range. We define a new gravity-sensitive spectral index (TLI-g) that consistently separates young from field objects, showing a performance superior to other indices from the literature. Even better separation between the two classes can be achieved through machine learning methods which use the entire NIR spectra as an input. Moreover, we show that the H- and K-bands alone are enough for this purpose. Finally, we evaluate the relative importance of different spectral regions for gravity classification as returned by the machine learning models. We find that the H-band broad-band shape is the most relevant feature, followed by the FeH absorption bands at 1.2um and 1.24um and the KI doublet at 1.24.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/3089
- Title:
- Young clumps embedded in IRDC
- Short Name:
- J/MNRAS/451/3089
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of starless and protostellar clumps associated with infrared dark clouds (IRDCs) in a 40 degrees wide region of the inner Galactic plane (|b|<=1). We have extracted the far-infrared (FIR) counterparts of 3493 IRDCs with known distance in the Galactic longitude range 15<=l<=55 and searched for the young clumps using Herschel infrared Galactic plane survey, the survey of the Galactic plane carried out with the Herschel satellite. Each clump is identified as a compact source detected at 160, 250 and 350um. The clumps have been classified as protostellar or starless, based on their emission (or lack of emission) at 70um. We identify 1723 clumps, 1056 (61%) of which are protostellar and 667 (39%) starless. These clumps are found within 764 different IRDCs, 375 (49%) of which are only associated with protostellar clumps, 178 (23%) only with starless clumps, and 211 (28%) with both categories of clumps. The clumps have a median mass of ~250M_{sun}_ and range up to >10^4^M_{sun}_ in mass and up to 10^5^L_{sun}_ in luminosity. The mass-radius distribution shows that almost 30% of the starless clumps identified in this survey could form high-mass stars; however these massive clumps are confined in only 4% of the IRDCs. Assuming a minimum mass surface density threshold for the formation of high-mass stars, the comparison of the numbers of massive starless clumps and those already containing embedded sources suggests an upper limit lifetime for the starless phase of ~10^5^yr for clumps with a mass M>500M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/124
- Title:
- Young star forming region NGC 2264 Spitzer sources
- Short Name:
- J/ApJ/794/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer 3.6, 4.5, 5.8, 8.0, and 24 {mu}m images of the Mon OB1 East giant molecular cloud, which contains the young star forming region NGC 2264, as well as more extended star formation. With Spitzer data and Two Micron All Sky Survey photometry, we identify and classify young stellar objects (YSOs) with dusty circumstellar disks and/or envelopes in Mon OB1 East by their infrared-excess emission and study their distribution with respect to cloud material. We find a correlation between the local surface density of YSOs and column density of molecular gas as traced by dust extinction that is roughly described as a power law in these quantities. NGC 2264 follows a power-law index of ~2.7, exhibiting a large YSO surface density for a given gas column density. Outside of NGC 2264 where the surface density of YSOs is lower, the power law is shallower and the region exhibits a larger gas column density for a YSO surface density, suggesting the star formation is more recent. In order to measure the fraction of cloud members with circumstellar disks/envelopes, we estimate the number of diskless pre-main-sequence stars by statistical removal of background star detections. We find that the disk fraction of the NGC 2264 region is 45%, while the surrounding, more distributed regions show a disk fraction of 19%. This may be explained by the presence of an older, more dispersed population of stars. In total, the Spitzer observations provide evidence for heterogenous, non-coeval star formation throughout the Mon OB1 cloud.
- ID:
- ivo://CDS.VizieR/J/MNRAS/404/661
- Title:
- Young stellar outflows near-IR imaging
- Short Name:
- J/MNRAS/404/661
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a near-infrared imaging survey of luminous young stellar outflow candidates using the United Kingdom Infrared Telescope. Observations were obtained in the broad band K (2.2um) and through narrow band filters at the wavelengths of H_2_ v=1-0 S(1) (2.1218um) and Br gamma (2.166um) lines. Fifty regions were imaged with a field of view of 2.2x2.2arcmin^2^. Several young embedded clusters are unveiled in our near-infrared images. 76% of the objects exhibit H_2_ emission and 50% or more of the objects exhibit aligned H_2_ emission features suggesting collimated outflows, many of which are new detections. These observations suggest that disk accretion is probably the leading mechanism in the formation of stars, at least up to late O spectral types. The young stellar objects responsible for many of these outflows are positively identified in our images based on their locations with respect to the outflow lobes, 2MASS colours and association with MSX, IRAS, millimetre and radio sources. The close association of molecular outflows detected in CO with the H_2_ emission features produced by shock excitation by jets from the young stellar objects suggests that the outflows from these objects are jet-driven. Towards strong radio emitting sources, H_2_ jets were either not detected or were weak when detected, implying that most of the accretion happens in the pre-UCHII phase; accretion and outflows are probably weak when the YSO has advanced to its UCHII stage.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A57
- Title:
- Young visual M-dwarf binaries spectra
- Short Name:
- J/A+A/642/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from an integral field spectroscopy study of seven close visual binary pairs of young M-dwarf multiple systems. The target systems are part of the astrometric monitoring AstraLux program, surveying hundreds of M-dwarf systems for multiplicity and obtaining astrometric epochs for orbital constraints. Our new VLT/SINFONI data provides resolved spectral type classification in the J, H and K bands for seven of these low-mass M-dwarf binaries, which we determine by comparing them to empirical templates and examining the strength of water absorption in the K-band. The medium resolution K-band spectra also allows us to derive effective temperatures for the individual components. All targets in the survey display several signs of youth, and some have kinematics similar to young moving groups, or low surface gravities which we determine from measuring equivalent widths of gravity sensitive alkali lines in the J-band. Resolved photometry from our targets is also compared with isochrones from theoretical evolutionary models, further implying young ages. Dynamical masses will be provided from ongoing monitoring of these systems, which can be seen as emblematic binary benchmarks that may be used to calibrate evolutionary models for low-mass stars in the future.
- ID:
- ivo://CDS.VizieR/J/A+A/599/A37
- Title:
- YSO candidates in IRAS 20319+3958
- Short Name:
- J/A+A/599/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globules and pillars, impressively revealed by the Spitzer and Herschel satellites, for example, are pervasive features found in regions of massive star formation. Studying their embedded stellar populations can provide an excellent laboratory to test theories of triggered star formation and the features that it may imprint on the stellar aggregates resulting from it. We studied the globule IRAS 20319+3958 in Cygnus X by means of visible and near-infrared imaging and spectroscopy, complemented with mid-infrared Spitzer/IRAC imaging, in order to obtain a census of its stellar content and the nature of its embedded sources. Our observations show that the globule contains an embedded aggregate of about 30 very young (<~1Myr) stellar objects, for which we estimate a total mass of ~90M_{sun}_. The most massive members are three systems containing early B-type stars. Two of them most likely produced very compact HII regions, one of them being still highly embedded and coinciding with a peak seen in emission lines characterising the photon dominated region (PDR). Two of these three systems are resolved binaries, and one of those contains a visible Herbig Be star. An approximate derivation of the mass function of the members of the aggregate gives hints of a slope at high masses shallower than the classical Salpeter slope, and a peak of the mass distribution at a mass higher than that at which the widely adopted log-normal initial mass function peaks. The emission distribution of H_2_ and Brackett gamma, tracing the PDR and the ionised gas phase, respectively, suggests that molecular gas is distributed as a shell around the embedded aggregate, filled with centrally-condensed ionised gas. Both, the morphology and the low excitation of the HII region, indicate that the sources of ionisation are the B stars of the embedded aggregate, rather than the external UV field caused by the O stars of Cygnus OB2. The youth of the embedded cluster, combined with the isolation of the globule, suggests that star formation in the globule was triggered by the passage of the ionisation front.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1145
- Title:
- YSO near-infrared properties
- Short Name:
- J/AJ/130/1145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution (R~18000), high signal-to-noise ratio, 2{mu}m spectra of 52 IR-selected Class I and flat-spectrum young stellar objects in the Taurus-Auriga, {rho} Ophiuchi, Serpens, Perseus, and Corona Australis dark clouds. We detect key absorption lines in 41 objects and fit synthetic spectra generated from pre-main-sequence models to deduce the effective temperatures, surface gravities, near-IR veilings, rotation velocities, and radial velocities of each of these 41 sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/702/178
- Title:
- YSOs in the central 400pc of the Galaxy
- Short Name:
- J/ApJ/702/178
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The central kpc of the Milky Way might be expected to differ significantly from the rest of the Galaxy with regard to gasdynamics and the formation of young stellar objects (YSOs). We probe this possibility with mid-infrared observations obtained with Infrared Array Camera and Multiband Imaging Photometer on Spitzer and with Midcourse Space Experiment. We use color-color diagrams and spectral energy distribution (SED) fits to explore the nature of YSO candidates (including objects with 4.5um excesses possibly due to molecular emission). We use the SEDs of these sources to estimate their physical characteristics; their masses appear to range from ~10 to ~20M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/A+A/362/199
- Title:
- YSOs in the l=+45 ISOGAL field
- Short Name:
- J/A+A/362/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 7 and 15{mu}m observations of the Galaxy obtained by the ISOGAL program offer an unique possibility to investigate and separate the different populations of stars in the Galactic Plane, in particular to study the population of low flux density YSOs which could not be detected with IRAS.
- ID:
- ivo://CDS.VizieR/J/ApJ/714/778
- Title:
- YSOs in the Serpens Molecular Cloud
- Short Name:
- J/ApJ/714/778
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer InfraRed Spectrograph (IRS) mid-infrared (5-35um) spectra of a complete flux-limited sample (>=3mJy at 8um) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and classified. Background stars (with slope consistent with a reddened stellar spectrum and silicate features in absorption), galaxies (with redshifted polycyclic aromatic hydrocarbon (PAH) features), and a planetary nebula (with high ionization lines) amount to 22% of contamination in this sample, leaving 115 true YSOs. Sources with rising spectra and ice absorption features, classified as embedded Stage I protostars, amount to 18% of the sample. The remaining 82% (94) of the disk sources are analyzed in terms of spectral energy distribution shapes, PAHs, and silicate features. The presence, strength, and shape of these silicate features are used to infer disk properties for these systems. About 8% of the disks have 30/13um flux ratios consistent with cold disks with inner holes or gaps, and 3% of the disks show PAH emission.
