- ID:
- ivo://CDS.VizieR/J/MNRAS/437/1561
- Title:
- DR 21 Chandra source catalogue
- Short Name:
- J/MNRAS/437/1561
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied the young low-mass pre-main sequence (PMS) stellar population associated with the massive star-forming region DR 21 by using archival X-ray Chandra observations and by complementing them with existing optical and infrared (IR) surveys. The Chandra observations have revealed for the first time a new highly extincted population of PMS low-mass stars previously missed in observations at other wavelengths. The X-ray population exhibits three main stellar density peaks, coincident with the massive star-forming regions, being the DR 21 core the main peak. The cross-correlated X-ray/IR sample exhibits a radial 'Spokes-like' stellar filamentary structure that extends from the DR 21 core towards the northeast. The near-IR data reveal a centrally peaked structure for the extinction, which exhibits its maximum in the DR 21 core and gradually decreases with the distance to the N-S cloud axis and to the cluster centre. We find evidence of a global mass segregation in the full low-mass stellar cluster, and of a stellar age segregation, with the youngest stars still embedded in the N-S cloud, and more evolved stars more spatially distributed. The results are consistent with the scenario where an elongated overall potential well created by the full low-mass stellar cluster funnels gas through filaments feeding stellar formation. Besides the full gravitational well, smaller scale local potential wells created by dense stellar sub-clusters of low-mass stars are privileged in the competition for the gas of the common reservoir, allowing the formation of massive stars. We also discuss the possibility that a stellar collision in the very dense stellar cluster revealed by Chandra in the DR 21 core is the origin of the large-scale and highly energetic outflow arising from this region.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/619/A106
- Title:
- 3D shape of Orion A from Gaia DR2
- Short Name:
- J/A+A/619/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Gaia DR2 distances of about 700 mid-infrared selected young stellar objects in the benchmark giant molecular cloud Orion A to infer its 3D shape and orientation. We find that Orion A is not the fairly straight filamentary cloud that we see in (2D) projection, but instead a cometary-like cloud oriented toward the Galactic plane, with two distinct components: a denser and enhanced star-forming (bent) Head, and a lower density and star-formation quieter ~75pc long Tail. The true extent of Orion A is not the projected ~40pc but ~90pc, making it by far the largest molecular cloud in the local neighborhood. Its aspect ratio (~30:1) and high column-density fraction (~45%) make it similar to large-scale Milky Way filaments ("bones"), despite its distance to the galactic mid-plane being an order of magnitude larger than typically found for these structures.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A85
- Title:
- 3D view of Taurus with Gaia and Herschel
- Short Name:
- J/A+A/638/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Taurus represents an ideal region to study the three-dimensional distribution of the young stellar population and relate it to the associated molecular cloud. The second Gaia data release (DR2) enables us to investigate the Taurus complex in three dimensions, starting from a previously defined robust membership. The molecular cloud structured in filaments can be traced in emission using the public far-infrared maps from Herschel. From a compiled catalog of spectroscopically confirmed members, we analyze the 283 sources with reliable parallax and proper motions in the Gaia DR2 archive. We fit the distribution of parallaxes and proper motions with multiple populations described by multivariate Gaussians. We compute the cartesian Galactic coordinates (X,Y,Z) and, for the populations associated with the main cloud, also the galactic space velocity (U,V,W). We discuss the spatial distribution of the populations in relation to the structure of the filamentary molecular cloud traced by Herschel. We discover the presence of six populations which are all well defined in parallax and proper motions, with the only exception being Taurus D. The derived distances range between ~130 and ~160pc. We do not find a unique relation between stellar population and the associated molecular cloud: while the stellar population seems to be on the cloud surface, both lying at similar distances, this is not the case when the molecular cloud is structured in filaments. Taurus B is probably moving in the direction of Taurus A, while Taurus E appears to be moving towards them. The Taurus region is the result of a complex star formation history which most probably occurred in clumpy and filamentary structures that are evolving independently.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/121
- Title:
- 127 early type and pre-main-sequence stars in W4
- Short Name:
- J/ApJ/899/121
- Date:
- 15 Mar 2022 03:47:36
- Publisher:
- CDS
- Description:
- Stellar kinematics provides the key to understanding the formation process and dynamical evolution of stellar systems. Here, we present a kinematic study of the massive star-forming region (SFR) W4 in the Cassiopeia OB6 association using the Gaia Data Release 2 and high-resolution optical spectra. This SFR is composed of a core cluster (IC1805) and a stellar population distributed over 20pc, which is a typical structural feature found in many OB associations. According to a classical model, this structural feature can be understood in the context of the dynamical evolution of a star cluster. The core-extended structure exhibits internally different kinematic properties. Stars in the core have an almost isotropic motion, and they appear to reach virial equilibrium given their velocity dispersion (0.9{+/-}0.3km/s) comparable to that in a virial state (~0.8km/s). On the other hand, the distributed population shows a clear pattern of radial expansion. From the N-body simulation for the dynamical evolution of a model cluster in subvirial state, we reproduce the observed structure and kinematics of stars. This model cluster experiences collapse for the first 2Myr. Some members begin to radially escape from the cluster after the initial collapse, eventually forming a distributed population. The internal structure and kinematics of the model cluster appear similar to those of W4. Our results support the idea that the stellar population distributed over 20pc in W4 originate from the dynamical evolution of IC1805.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/2220
- Title:
- Early-type Sco-Cen members with literature RVs
- Short Name:
- J/MNRAS/453/2220
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the serendipitous discovery of several young mid-M stars found during a search for new members of the 30-40Myr-old Octans Association. Only one of the stars may be considered a possible Octans(-Near) member. However, two stars have proper motions, kinematic distances, radial velocities, photometry and LII {lambda}6708 measurements consistent with membership in the 8-10Myr-old TW Hydrae Association. Another may be an outlying member of TW Hydrae but has a velocity similar to that predicted by membership in Octans. We also identify two new lithium-rich members of the neighbouring Scorpius-Centaurus OB Association (Sco-Cen). Both exhibit large 12 and 22{mu}m excesses and strong, variable H{alpha} emission which we attribute to accretion from circumstellar discs. Such stars are thought to be incredibly rare at the ~16Myr median age of Sco-Cen and they join only one other confirmed M-type and three higher mass accretors outside of Upper Scorpius. The serendipitous discovery of two accreting stars hosting large quantities of circumstellar material may be indicative of a sizeable age spread in Sco-Cen, or further evidence that disc dispersal and planet formation time-scales are longer around lower mass stars. To aid future studies of Sco-Cen, we also provide a newly compiled catalogue of 305 early-type Hipparcos members with spectroscopic radial velocities sourced from the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A164
- Title:
- Edge-on protoplanetary disks ALMA images
- Short Name:
- J/A+A/642/A164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to study vertical settling and radial drift of dust in protoplanetary disks from a different perspective: an edge-on view. An estimation of the amplitude of settling and drift is highly relevant to understanding planet formation. We analyze a sample of 12 HST-selected edge-on protoplanetary disks for which the vertical extent of the emission layers can be constrained directly. We present ALMA high angular resolution continuum images (0.1arcsec) of these disks at two wavelengths, 0.89mm and 2.06mm (respectively ALMA bands 7 and 4), supplemented with archival band 6 data (1.33mm) where available. For most sources, the millimeter continuum emission is more compact than the scattered light, both in the vertical and radial directions. Six sources are resolved along their minor axis in at least one millimeter band, providing direct information on the vertical distribution of the millimeter grains. For the second largest disk of the sample, the significant difference in vertical extent between band 7 and band 4 suggests efficient size-selective vertical settling of large grains. Furthermore, the only Class I object in our sample shows evidence of flaring in the millimeter. Along the major axis, all disks are well resolved. Four of them are larger in band 7 than in band 4 in the radial direction, and three have a similar radial extent in all bands. For all disks, we derive the millimeter brightness temperature and spectral index maps. We find that the disks are likely optically thick and that the dust emission reveals low brightness temperatures in most cases (<10K). The integrated spectral indices are similar to those of disks at lower inclination. The comparison of a generic radiative transfer disk model with our data shows that at least 3 disks are consistent with a small millimeter dust scale height, of a few au (measured at r=100au). This is in contrast with the more classical value of h_g_~10au derived from scattered light images and from gas line measurements. These results confirm, by direct observations, that large (millimeter) grains are subject to significant vertical settling in protoplanetary disks.
- ID:
- ivo://CDS.VizieR/J/ApJ/626/446
- Title:
- Effective temperature scale of FGK stars
- Short Name:
- J/ApJ/626/446
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The infrared flux method (IRFM) has been applied to a sample of 135 dwarf and 36 giant stars covering the following regions of the atmospheric parameter space: (1) the metal-rich ([Fe/H]>~0) end (consisting mostly of planet-hosting stars), (2) the cool (Teff<~5000K) metal-poor (-1<~[Fe/H]<~-3) dwarf region, and (3) the very metal-poor ([Fe/H]<~-2.5) end.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A87
- Title:
- Ejection processes in NGC 2264
- Short Name:
- J/A+A/620/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study of forbidden [OI]6300{AA} emission line profiles in classical T Tauri stars in the young, open cluster NGC 2264. We separate each of these profiles into up to four features via Gaussian decomposition: narrow and broad low-velocity components and blue- and redshifted high-velocity components. We study the luminosities and kinematic properties of these components along with known stellar and accretion parameters, in order to investigate their origins.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A67
- Title:
- Embedded YSOs in Carina Nebula complex
- Short Name:
- J/A+A/549/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Carina Nebula represents one of the largest and most active star forming regions known in our Galaxy. It contains numerous very massive (M>~40M_{sun}) stars that strongly act the surrounding clouds by their ionizing radiation and stellar winds. Our recently obtained Herschel PACS & SPIRE far-infrared maps cover the full area (~~8.7{deg}^2^) of the Carina Nebula complex and reveal the population of deeply embedded young stellar objects, most of which are not yet visible in the mid- or near-infrared. We study the properties of the 642 objects that are independently detected as point-like sources in at least two of the five Herschel bands. For those objects that can be identified with apparently single Spitzer counterparts, we use radiative transfer models to derive information about the basic stellar and circumstellar parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A30
- Title:
- Emission line flux densities for 12 YSOs
- Short Name:
- J/A+A/631/A30
- Date:
- 28 Oct 2021 07:35:47
- Publisher:
- CDS
- Description:
- Episodic accretion plays an important role in the evolution of young stars. Although it has been under investigation for a long time, the origin of such episodic accretion events is not yet understood. We investigate the dust and gas emission of a sample of young outbursting sources in the infrared to get a better understanding of their properties and circumstellar material, and we use the results in a further work to model the objects. We used Herschel data, from our PI program of 12 objects and complemented with archival observations to obtain the spectral energy distributions (SEDs) and spectra of our targets. We report here the main characteristics of our sample, focussing on the SED properties and on the gas emission lines detected in the PACS and SPIRE spectra. The SEDs of our sample show the diversity of the outbursting sources, with several targets showing strong emission in the far-infrared from the embedded objects. Most of our targets reside in a complex environment, which we discuss in detail. We detected several atomic and molecular lines, in particular rotational CO emission from several transitions from J=38-37 to J=4-3. We constructed rotational diagrams for the CO lines, and derived in three domains of assumed local thermodynamic equilibrium (LTE) temperatures and column densities, ranging mainly between 0-100K and 400-500K. We confirm correlation in our sample between intense CO J=16-15 emission and the column density of the warm domain of CO, N(warm). We notice a strong increase in luminosity of HH 381 IRS and a weaker increase for PP 13 S, which shows the beginning of an outburst.
