- ID:
- ivo://CDS.VizieR/J/ApJ/805/57
- Title:
- Atmosphere parameters model-derived for PMS & BDs
- Short Name:
- J/ApJ/805/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We test state-of-the-art model atmospheres for young very-low-mass stars and brown dwarfs in the infrared, by comparing the predicted synthetic photometry over 1.2-24{mu}m to the observed photometry of M-type spectral templates in star-forming regions. We find that (1) in both early and late young M types, the model atmospheres imply effective temperatures (Teff) several hundred Kelvin lower than predicted by the standard pre-main sequence (PMS) spectral type-Teff conversion scale (based on theoretical evolutionary models). It is only in the mid-M types that the two temperature estimates agree. (2) The Teff discrepancy in the early M types (corresponding to stellar masses >~0.4M_{sun}_ at ages of a few Myr) probably arises from remaining uncertainties in the treatment of atmospheric convection within the atmospheric models, whereas in the late M types it is likely due to an underestimation of dust opacity. (3) The empirical and model-atmosphere J-band bolometric corrections are both roughly flat, and similar to each other, over the M-type Teff range. Thus the model atmospheres yield reasonably accurate bolometric luminosities (Lbol), but lead to underestimations of mass and age relative to evolutionary expectations (especially in the late M types) due to lower Teff. We demonstrate this for a large sample of young Cha I and Taurus sources. (4) The trends in the atmospheric model J-K_s_ colors, and their deviations from the data, are similar at PMS and main sequence ages, suggesting that the model dust opacity errors we postulate here for young ages also apply at field ages.
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- ID:
- ivo://CDS.VizieR/J/ApJ/764/133
- Title:
- Auriga-California giant molecular cloud
- Short Name:
- J/ApJ/764/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/55
- Title:
- AzTEC/ASTE survey at 1.1mm toward the SMC
- Short Name:
- J/ApJ/835/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first 1.1mm continuum survey toward the Small Magellanic Cloud (SMC) was performed using the AzTEC instrument installed on the ASTE 10m telescope. This survey covered 4.5deg^2^ of the SMC with 1{sigma} noise levels of 5-12mJy/beam, and 44 extended objects were identified. The 1.1mm extended emission has good spatial correlation with Herschel 160{mu}m, indicating that the origin of the 1.1mm extended emission is thermal emission from a cold dust component. We estimated physical properties using the 1.1mm and filtered Herschel data (100, 160, 250, 350, and 500{mu}m). The 1.1mm objects show dust temperatures of 17-45K and gas masses of 4x10^3^-3x10^5^M_{sun}_, assuming single-temperature thermal emission from the cold dust with an emissivity index, {beta}, of 1.2 and a gas-to-dust ratio of 1000. These physical properties are very similar to those of giant molecular clouds (GMCs) in our galaxy and the Large Magellanic Cloud. The 1.1mm objects also displayed good spatial correlation with the Spitzer 24{mu}m and CO emission, suggesting that the 1.1mm objects trace the dense gas regions as sites of massive star formation. The dust temperature of the 1.1mm objects also demonstrated good correlation with the 24{mu}m flux connected to massive star formation. This supports the hypothesis that the heating source of the cold dust is mainly local star-formation activity in the 1.1mm objects. The classification of the 1.1mm objects based on the existence of star-formation activity reveals the differences in the dust temperature, gas mass, and radius, which reflects the evolution sequence of GMCs.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/23
- Title:
- BANYAN. XI. The BANYAN {Sigma} algorithm
- Short Name:
- J/ApJ/856/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BANYAN {Sigma} is a new Bayesian algorithm to identify members of young stellar associations within 150pc of the Sun. It includes 27 young associations with ages in the range ~1-800Myr, modeled with multivariate Gaussians in six-dimensional (6D) XYZUVW space. It is the first such multi-association classification tool to include the nearest sub-groups of the Sco-Cen OB star-forming region, the IC2602, IC2391, Pleiades and Platais 8 clusters, and the {rho} Ophiuchi, Corona Australis, and Taurus star formation regions. A model of field stars is built from a mixture of multivariate Gaussians based on the Besancon Galactic model. The algorithm can derive membership probabilities for objects with only sky coordinates and proper motion, but can also include parallax and radial velocity measurements, as well as spectrophotometric distance constraints from sequences in color-magnitude or spectral type-magnitude diagrams. BANYAN {Sigma} benefits from an analytical solution to the Bayesian marginalization integrals over unknown radial velocities and distances that makes it more accurate and significantly faster than its predecessor BANYAN II. A contamination versus hit rate analysis is presented and demonstrates that BANYAN {Sigma} achieves a better classification performance than other moving group tools available in the literature, especially in terms of cross-contamination between young associations. An updated list of bona fide members in the 27 young associations, augmented by the Gaia-DR1 release, as well as all parameters for the 6D multivariate Gaussian models for each association and the Galactic field neighborhood within 300 pc are presented.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A64
- Title:
- Barn 335 ALMA datacubes
- Short Name:
- J/A+A/631/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relationship between outflow launching and the formation of accretion disks around young stellar objects is still not entirely understood, which is why spectrally and spatially resolved observations are needed. Recently, the Atacama Large Millimetre/ sub-millimetre Array (ALMA) carried out long-baseline observations towards a handful of young sources, revealing connections between outflows and the inner regions of disks. Here we aim to determine the small-scale kinematical and morphological properties of the outflow from the isolated protostar B335 for which no Keplerian disk has, so far, been observed on scales down to 10au. We used ALMA in its longest-baseline configuration to observe emission from CO isotopologues, SiO, SO_2_, and CH_3_OH. The proximity of B335 provides a resolution of ~3au (0.03"). We also combined our long-baseline data with archival observations to produce a high-fidelity image covering scales up to 700 au (7"). ^12^CO has an X-shaped morphology with arms ~50au in width that we associate with the walls of an outflow cavity, similar to what is observed on larger scales. Long-baseline continuum emission is confined to <7au from the protostar, while short- baseline continuum emission follows the ^12^CO outflow and cavity walls. Methanol is detected within ~30au of the protostar. SiO is also detected in the vicinity of the protostar, but extended along the outflow. The ^12^CO outflow does not show any clear signs of rotation at distances >=30au from the protostar. SiO traces the protostellar jet on small scales, but without obvious rotation. CH_3_OH and SO_2_ trace a region <16au in diameter, centred on the continuum peak, which is clearly rotating. Using episodic, high-velocity, ^12^CO features, we estimate the launching radius of the outflow to be<0.1au and dynamical timescales of the order of a few years.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A56
- Title:
- [BHB2007] 11 full stokes continuum ALMA images
- Short Name:
- J/A+A/616/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Polarized continuum emission at millimeter/sub-millimeter wavelengths is usually attributed to thermal emission from dust grains aligned through radiative torques with the magnetic field. However, recent theoretical work has shown that under specific conditions polarization may arise from self-scattering of thermal emission and by radiation fields from a nearby stellar object. We use multi-frequency polarization observations of a circumbinary disk to investigate how the polarization properties change at distinct frequency bands. Our goal is to discern the main mechanism responsible for the polarization through comparison between our observations and model predictions for each of the proposed mechanisms. We used the Atacama Large Millimeter/submillimeter Array to perform full polarization observations at 97.5GHz (Band 3), 233GHz (Band 6) and 343.5GHz (Band 7). The ALMA data have a mean spatial resolution of 28AU. The target is the Class I object BHB07-11, which is the youngest object in the Barnard 59 protocluster. Complementary Karl G. Jansky Very Large Array observations at 34.5GHz were also performed and revealed a binary system at centimetric continuum emission within the disk. We detect an extended and structured polarization pattern remarkably consistent among all three bands. The distribution of polarized intensity resembles a horseshoe shape with polarization angles following this morphology. From the spectral index between bands 3 and 7, we derive a dust opacity index beta ~1 consistent with maximum grain sizes larger than expected to produce self-scattering polarization in each band. The polarization morphology and the polarization levels do not match predictions from self-scattering. On the other hand, marginal correspondence is seen between our maps and predictions from radiation field assuming the brightest binary component as main radiation source. Previous molecular line data from BHB07-11 indicates disk rotation. We used the DustPol module of the ARTIST radiative transfer tool to produce synthetic polarization maps from a rotating magnetized disk model assuming combined poloidal and toroidal magnetic field components. The magnetic field vectors (i. e., the polarization vectors rotated by 90 degrees) are better represented by a model with poloidal magnetic field strength about 3 times the toroidal one. The similarity of our polarization patterns among the three bands provides a strong evidence against self-scattering and radiation fields. On the other hand, our data are reasonably well reproduced by a model of disk with toroidal magnetic field components slightly smaller than poloidal ones. The residual is likely due to the internal twisting of the magnetic field due to the binary system dynamics, which is not considered in our model.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A8
- Title:
- Binary central stars of SMC PNe
- Short Name:
- J/A+A/561/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Optical Gravitational Lensing Experiment (OGLE), originally designed to search for microlensing events, provides a rich and uniform data set suitable for studying the variability of certain types of objects. We used the OGLE data to study the photometry of central stars of planetary nebulae (PNe) in the Small Magellanic Cloud (SMC). In particular, we searched for close binary central stars with the aim to constrain the binary fraction and period distribution in the SMC. We also searched for PNe mimics and removed them from the PNe sample. We identified 52 counterparts of PNe in the SMC in the I-band images from the OGLE-II and OGLE-III surveys. We analysed the time-series photometry of the PNe. Spectra of the photometric variables were obtained to constrain the nature of the objects or search for additional evidence for binarity. Eight variables were found. Of these, seven objects are PNe mimics, including one symbiotic star candidate. One close binary central star of PN with a period of 1.15 or 2.31 day was discovered. The obtained binary fraction for the SMC PNe and the observational biases are discussed in terms of the OGLE observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/745/19
- Title:
- Binary systems in Taurus-Auriga
- Short Name:
- J/ApJ/745/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The past decade has seen a revolution in our understanding of protoplanetary disk evolution and planet formation in single-star systems. However, the majority of solar-type stars form in binary systems, so the impact of binary companions on protoplanetary disks is an important element in our understanding of planet formation. We have compiled a combined multiplicity/disk census of Taurus-Auriga, plus a restricted sample of close binaries in other regions, in order to explore the role of multiplicity in disk evolution. Our results imply that the tidal influence of a close (<=40AU) binary companion significantly hastens the process of protoplanetary disk dispersal, as ~2/3 of all close binaries promptly disperse their disks within <~1Myr after formation. However, prompt disk dispersal only occurs for a small fraction of wide binaries and single stars, with ~80%-90% retaining their disks for at least ~2-3Myr (but rarely for more than ~5Myr). Our new constraints on the disk clearing timescale have significant implications for giant planet formation; most single stars have 3-5Myr within which to form giant planets, whereas most close binary systems would have to form giant planets within <~1Myr. If core accretion is the primary mode for giant planet formation, then gas giants in close binaries should be rare. Conversely, since almost all single stars have a similar period of time within which to form gas giants, their relative rarity in radial velocity (RV) surveys indicates either that the giant planet formation timescale is very well matched to the disk dispersal timescale or that features beyond the disk lifetime set the likelihood of giant planet formation.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A14
- Title:
- Blind photometric study of NGC 2264 region
- Short Name:
- J/A+A/621/A14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to their extensive and homogeneous sky coverage, deep, large-scale, multi-wavelength surveys are uniquely suited to statistically identify and map young star clusters in our Galaxy. Such studies are crucial to address themes like the initial mass function, or the modes and dynamics of star cluster formation and evolution. We aim to test a purely photometric approach to statistically identify a young clustered population embedded in a large population of field stars, with no prior knowledge on the nature of stars in the field. We conducted our blind test study on the NGC 2264 region, which hosts a well-known, richly populated young cluster (~3Myr-old) and several active star-forming sites. We selected a large (4 deg^2^) area around the NGC 2264 cluster, and assembled an extensive r, i, J catalog of the field from pre-existing large-scale surveys, notably Pan-STARRS1 and UKIDSS. We then mapped the stellar color locus on the (i-J, r-i) diagram to select M-type stars, which offer the following observational advantages with respect to more massive stars: i) they comprise a significant fraction of the Galactic stellar population; ii) their pre-main sequence phase lasts significantly longer than for higher-mass stars; iii) they exhibit the strongest luminosity evolution from the pre-main sequence to the main sequence; iv) their observed r, i, J colors provide a direct and empirical estimate of AV. A comparative analysis of the photometric and spatial properties of M-type stars as a function of AV enabled us to probe the structure and stellar content of our field. Using only r, i, J photometry, we could identify two distinct populations in our field: a diffuse field population and a clustered population in the center of the field. The presence of a concentration of occulting material, spatially associated with the clustered population, allowed us to derive an estimate of its distance (800-900pc) and age (0.5-5Myr); these values are overall consistent with the literature parameters for the NGC 2264 star-forming region. The extracted clustered population exhibits a hierarchical structure, with two main clumps and peaks in number density of objects around the most extincted locations within the field. An excellent agreement is found between the observed substructures for the clustered population and a map of the NGC 2264 subregions reported in the literature. Our selection of clustered members is coherent with the literature census of the NGC 2264 cluster for about 95% of the objects located in the inner regions of the field, where the estimated contamination rate by field stars in our sample is only 2%. In addition, the availability of a uniform dataset for a large area around the NGC 2264 region enabled us to discover a population of about a hundred stars with indications of statistical membership to the cluster, therefore extending the low-mass population census of NGC 2264 to distances of 10-15pc from the cluster cores. By making use solely of deep, multi-band (r, i, J) photometry, without assuming any further knowledge on the stellar population of our field, we were able to statistically identify and reconstruct the structure of a very young cluster that has been a prime target for star formation studies over several decades. The method tested here can be readily applied to surveys such as Pan-STARRS and the future LSST to undertake a first complete census of low-mass, young stellar populations down to distances of several kpc across the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/1202
- Title:
- BVI photometry in W5E HII region
- Short Name:
- J/MNRAS/415/1202
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this paper is to present the results of photometric investigations of the central cluster of the W5 E HII region as well as a follow-up study of the triggered star formation in and around bright-rimmed clouds (BRCs). We have carried out wide-field UBVIc and deep VIc photometry of the W5 E HII region. A distance of ~2.1kpc and a mean age of ~1.3Myr have been obtained for the central cluster. The young stellar objects (YSOs) associated with the region are identified on the basis of near-infrared and mid-infrared observations.
