- 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.
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- 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/432/3445
- Title:
- YSOs on HII complex Sh2-252
- Short Name:
- J/MNRAS/432/3445
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The optically bright, extended HII region Sh2-252 is a part of the Gemini OB1 association. This region is mainly composed of two small clusters NGC 2175s and Teu 136 and four CHII regions namely A, B, C and E. In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population, its characteristics, spatial distribution, morphology of the region and finally to understand the star formation scenario of the complex for the first time. Spitzer-IRAC, MIPS photometry (3.6-24um) are combined with 2MASS-NIR and optical data sets to identify and classify the YSOs by their IR excess emission from their circumstellar material. From the well-fit models for each source derived from the SED fitting tool, we calculated the {chi}^2^ weighted model parameters such as the stellar mass (M*), temperature (T*), stellar age (t*), mass of the disc (Mdisc), disc accretion rate (dMdisc/dt), envelope accretion rate (dMenv/dt) presented in table1.dat.
- ID:
- ivo://CDS.VizieR/J/AJ/150/145
- Title:
- YSOVAR infrared photometry in GGD12-15
- Short Name:
- J/AJ/150/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an IR-monitoring survey with the Spitzer Space Telescope of the star-forming region GGD 12-15. More than 1000 objects were monitored, including about 350 objects within the central 5', which is found to be especially dense in cluster members. The monitoring took place over 38 days and is part of the Young Stellar Object VARiability project. The region was also the subject of a contemporaneous 67 ks Chandra observation. The field includes 119 previously identified pre-main sequence star candidates. X-rays are detected from 164 objects, 90 of which are identified with cluster members. Overall, we find that about half the objects in the central 5' are young stellar objects (YSOs) based on a combination of their spectral energy distribution, IR variability, and X-ray emission. Most of the stars with IR excess relative to a photosphere show large amplitude (>0.1 mag) mid-infrared (mid-IR) variability. There are 39 periodic sources, and all but one is found to be a cluster member. Almost half of the periodic sources do not show IR excesses. Overall, more than 85% of the Class I, flat spectrum, and Class II sources are found to vary. The amplitude of the variability is larger in more embedded YSOs. Most of the Class I/II objects exhibit redder colors in a fainter state, which is compatible with time-variable extinction. A few become bluer when fainter, which can be explained with significant changes in the structure of the inner disk. A search for changes in the IR due to X-ray events is carried out, but the low number of flares prevented an analysis of the direct impact of X-ray flares on the IR light curves. However, we find that X-ray detected Class II sources have longer timescales for change in the MIR than a similar set of non-X-ray detected Class IIs.
- ID:
- ivo://CDS.VizieR/J/AJ/140/1919
- Title:
- Zero point spectral energy distribution
- Short Name:
- J/AJ/140/1919
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The absolutely calibrated infrared (IR) stellar spectra of standard stars described by Engelke et al. are being extended into the visible and will span a continuous wavelength range from ~0.35um to 35.0um. This paper, which is a continuation of the series on calibration initiated with Cohen et al., presents the foundation of this extension. We find that due to various irregularities Vega ({alpha} Lyr) is not suitable for its traditional role as the primary visible or near-infrared standard star. We therefore define a new zero-point flux that is independent of Vega and, as far as is feasible, uses measured spectral energy distributions (SEDs) and fluxes derived from photometry. The calibrated primary stars now underpinning this zero-point definition are 109 Vir in the visible and Sirius ({alpha} CMa) in the infrared. The resulting zero-point SED tests well against solar analog data presented by Rieke et al. (2008, Cat. J/AJ/135/2245) while also maintaining an unambiguous link to specific calibration stars, thus providing a pragmatic range of options for any researcher wishing to tie it to a given set of photometry.
