- ID:
- ivo://CDS.VizieR/J/ApJ/831/125
- Title:
- ALMA 887{mu}m obs. of ChaI star-forming region
- Short Name:
- J/ApJ/831/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887{mu}m survey of the disk population around objects from ~2 to 0.03M_{sun}_ in the nearby ~2Myr old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887{mu}m flux densities into dust disk masses, hereafter M_dust_. We find that the M_dust_-M_*_ relation is steeper than linear and of the form M_dust_{propto}(M_*_)^1.3-1.9^, where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1-3 Myr old regions of Taurus, Lupus, and Chamaeleon I share the same M_dust_-M_*_ relation, while the 10 Myr old Upper Sco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/827/142
- Title:
- ALMA observations of GKM stars in Upper Sco
- Short Name:
- J/ApJ/827/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ALMA observations of 106 G-, K-, and M-type stars in the Upper Scorpius OB Association hosting circumstellar disks. With these data, we measure the 0.88mm continuum and ^12^CO J=3-2 line fluxes of disks around low-mass (0.14-1.66M_{sun}_) stars at an age of 5-11Myr. Of the 75 primordial disks in the sample, 53 are detected in the dust continuum and 26 in CO. Of the 31 disks classified as debris/evolved transitional disks, five are detected in the continuum and none in CO. The lack of CO emission in approximately half of the disks with detected continuum emission can be explained if CO is optically thick but has a compact emitting area (<~40au), or if the CO is heavily depleted by a factor of at least ~1000 relative to interstellar medium abundances and is optically thin. The continuum measurements are used to estimate the dust mass of the disks. We find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of M_dust_{propto}M_*_^1.67+/-0.37^. Disk dust masses in Upper Sco are compared to those measured in the younger Taurus star-forming region to constrain the evolution of disk dust mass. We find that the difference in the mean of log(M_dust_/M*) between Taurus and Upper Sco is 0.64+/-0.09, such that M_dust_/M* is lower in Upper Sco by a factor of ~4.5.
- ID:
- ivo://CDS.VizieR/J/AJ/153/240
- Title:
- ALMA survey of protoplanetary disks in sigma Ori
- Short Name:
- J/AJ/153/240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The {sigma} Orionis cluster is important for studying protoplanetary disk evolution, as its intermediate age (~3-5Myr) is comparable to the median disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas in 92 protoplanetary disks around {sigma} Orionis members with M_*_>~0.1M_{Sun}_. Our observations cover the 1.33mm continuum and several CO J=2-1 lines: out of 92 sources, we detect 37 in the millimeter continuum and 6 in ^12^CO, 3 in ^13^CO, and none in C^18^O. Using the continuum emission to estimate dust mass, we find only 11 disks with M_dust_>~10M_{Earth}_, indicating that after only a few Myr of evolution most disks lack sufficient dust to form giant planet cores. Stacking the individually undetected continuum sources limits their average dust mass to 5x lower than that of the faintest detected disk, supporting theoretical models that indicate rapid dissipation once disk clearing begins. Comparing the protoplanetary disk population in {sigma} Orionis to those of other star-forming regions supports the steady decline in average dust mass and the steepening of the M_dust_-M_*_ relation with age; studying these evolutionary trends can inform the relative importance of different disk processes during key eras of planet formation. External photoevaporation from the central O9 star is influencing disk evolution throughout the region: dust masses clearly decline with decreasing separation from the photoionizing source, and the handful of CO detections exist at projected separations of >1.5pc. Collectively, our findings indicate that giant planet formation is inherently rare and/or well underway by a few Myr of age.
- ID:
- ivo://CDS.VizieR/J/ApJ/752/58
- Title:
- {alpha} Per cluster members
- Short Name:
- J/ApJ/752/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because of its proximity to the Galactic plane, reliable identification of members of the {alpha} Persei cluster is often problematic. Based primarily on membership evaluations contained in six published papers, we constructed a mostly complete list of high-fidelity members of spectral type G and earlier that lie within 3 arc degrees of the cluster center. {alpha} Persei was the one nearby, rich, young open cluster not surveyed with the Spitzer Space Telescope. We examined the first and final data releases of the Wide-field Infrared Survey Explorer (WISE) and found 11, or perhaps 12, {alpha} Per cluster members that have excess mid-infrared emission above the stellar photosphere attributable to an orbiting dusty debris disk. The most unusual of these is V488 Per, a K-type star with an excess IR luminosity 16% (or more) of the stellar luminosity; this is a larger excess fraction than that of any other known dusty main-sequence star. Much of the dust that orbits V488 Per is at a temperature of ~800 K; if these grains radiate like blackbodies, then they lie only ~0.06 AU from the star. The dust is probably the aftermath of a collision of two planetary embryos or planets with small semimajor axes; such orbital radii are similar to those of many of the transiting planets discovered by the Kepler satellite.
- ID:
- ivo://CDS.VizieR/J/AJ/143/28
- Title:
- Analysis of B6-A9 stars from INES UV spectra
- Short Name:
- J/AJ/143/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Main-sequence (MS) and giant late-B and early-A type stars are the best targets for searching for nearby interstellar (IS) SiIV and CIV resonance lines because they are not able to produce them, either in atmospheric layers or in their circumstellar environment, and because many stars of these spectral types are nearby and located in the local interstellar medium (LISM). In addition, the use of certain stars hotter than B6 can lead to misinterpretations (e.g., alpha Arae). This work analyzes the reliable Short-Wavelength Prime (SWP) high-resolution UV spectra of 558 B6-A9 type stars observed by the International Ultraviolet Explorer at distances lower than 400pc from the Sun. For the first time, this work utilizes the entire INES database to extract stellar and IS information in a systematic way from homogeneous data. Stars were classified into seven groups: normal (MS and subgiant), giant, peculiar, emission line, Algols, pre-main sequence or Herbig Ae/Be, and shell stars. Only 10 normal stars, located beyond 90pc, show weak SiIV and CIV absorptions and are clustered around the direction of Sco-Cen, while 85 located closer than 90pc, as well as another 89 beyond 90pc, do not show any absorptions at all.
- ID:
- ivo://CDS.VizieR/J/AJ/155/34
- Title:
- Analysis of the NIR spectra of neighboring L dwarfs
- Short Name:
- J/AJ/155/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Discrepancies between competing optical and near-infrared (NIR) spectral typing systems for L dwarfs have motivated us to search for a classification scheme that ties the optical and NIR schemes together, and addresses complexities in the spectral morphology. We use new and extant optical and NIR spectra to compile a sample of 171 L dwarfs, including 27 low-gravity {beta} and {gamma} objects, with spectral coverage from 0.6-2.4 {mu}m. We present 155 new low-resolution NIR spectra and 19 new optical spectra. We utilize a method for analyzing NIR spectra that partially removes the broad-band spectral slope and reveals similarities in the absorption features between objects of the same optical spectral type. Using the optical spectra as an anchor, we generate near-infrared spectral average templates for L0-L8, L0-L4{gamma}, and L0-L1{beta} type dwarfs. These templates reveal that NIR spectral morphologies are correlated with the optical types. They also show the range of spectral morphologies spanned by each spectral type. We compare low-gravity and field-gravity templates to provide recommendations on the minimum required observations for credibly classifying low-gravity spectra using low-resolution NIR data. We use the templates to evaluate the existing NIR spectral standards and propose new ones where appropriate. Finally, we build on the work of Kirkpatrick et al. to provide a spectral typing method that is tied to the optical and can be used when only H or K band data are available. The methods we present here provide resolutions to several long-standing issues with classifying L dwarf spectra and could also be the foundation for a spectral classification scheme for cloudy exoplanets.
- ID:
- ivo://CDS.VizieR/III/166
- Title:
- A New Library of Optical Spectra
- Short Name:
- III/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Silva and Cornell have compiled a new digital optical stellar spectra library, consisting of intensities at 5A intervals between 3510A and 8930A for 72 different spectral types. These types range from O to M and luminosities range from I to V. Some weak-line and strong-line spectra are also included. The intensities are in ergs/A, normalized to 100 at 5450A.
- ID:
- ivo://CDS.VizieR/J/ApJ/894/5
- Title:
- APOGEE2-N NIR spectra of B-type stars
- Short Name:
- J/ApJ/894/5
- Date:
- 19 Jan 2022 00:59:33
- Publisher:
- CDS
- Description:
- We present a semi-empirical spectral classification scheme for normal B-type stars using near-infrared (NIR) spectra (1.5-1.7{mu}m) from the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment (APOGEE2)-N data release 14 (DR14) database. The main motivation for working with B-type stars is their importance in the evolution of young stellar clusters; however, we also take advantage of having a numerous sample (316 stars) of B-type star candidates in APOGEE2-N, for which we also have optical (3600-9100{AA}) counterparts from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey. By first obtaining an accurate spectral classification of the sources using the LAMOST DR3 spectra and the canonical spectral classification scheme, we found a linear relation between optical spectral types and the equivalent widths of the hydrogen lines of the Brackett series in the APOGEE2-N NIR spectra. This relation extends smoothly from a similar relation for O and early B stars found by Roman-Lopes+ (2018, J/ApJ/855/68). This way, we obtain a catalog of B-type sources with features in both the optical and NIR and a classification scheme refined down to one spectral subclass.
- ID:
- ivo://CDS.VizieR/J/ApJS/231/15
- Title:
- Astrometric monitoring of ultracool dwarf binaries
- Short Name:
- J/ApJS/231/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types M7-T5. Joint analysis of resolved imaging from Keck Observatory and Hubble Space Telescope and unresolved astrometry from CFHT/WIRCam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. As a result, we measure 38 precise individual masses spanning 30-115M_Jup_. We determine a model-independent substellar boundary that is ~70M_Jup_ in mass (~L4 in spectral type), and we validate Baraffe et al. evolutionary model predictions for the lithium-depletion boundary (60M_Jup_ at field ages). Assuming each binary is coeval, we test models of the substellar mass-luminosity relation and find that in the L/T transition, only the Saumon & Marley (2008ApJ...689.1327S) "hybrid" models accounting for cloud clearing match our data. We derive a precise, mass-calibrated spectral type-effective temperature relation covering 1100-2800K. Our masses enable a novel direct determination of the age distribution of field brown dwarfs spanning L4-T5 and 30-70M_Jup_. We determine a median age of 1.3Gyr, and our population synthesis modeling indicates our sample is consistent with a constant star formation history modulated by dynamical heating in the Galactic disk. We discover two triple-brown-dwarf systems, the first with directly measured masses and eccentricities. We examine the eccentricity distribution, carefully considering biases and completeness, and find that low-eccentricity orbits are significantly more common among ultracool binaries than solar-type binaries, possibly indicating the early influence of long-lived dissipative gas disks. Overall, this work represents a major advance in the empirical view of very low-mass stars and brown dwarfs.
- ID:
- ivo://CDS.VizieR/J/AJ/145/136
- Title:
- Astrometry and photometry of nearby white dwarfs
- Short Name:
- J/AJ/145/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the preliminary results of a survey aimed at significantly increasing the range and completeness of the local census of spectroscopically confirmed white dwarfs. The current census of nearby white dwarfs is reasonably complete only to about 20pc of the Sun, a volume that includes around 130 white dwarfs, a sample too small for detailed statistical analyses. This census is largely based on follow-up investigations of stars with very large proper motions. We describe here the basis of a method that will lead to a catalog of white dwarfs within 40pc of the Sun and north of the celestial equator, thus increasing by a factor of eight the extent of the northern sky census. White dwarf candidates are identified from the SUPERBLINK proper motion database, allowing us to investigate stars down to a proper motion limit {mu}>40mas/yr, while minimizing the kinematic bias for nearby objects. The selection criteria and distance estimates are based on a combination of color-magnitude and reduced proper motion diagrams. Our follow-up spectroscopic observation campaign has so far uncovered 193 new white dwarfs, among which we identify 127 DA (including 9 DA+dM and 4 magnetic), 1 DB, 56 DC, 3 DQ, and 6 DZ stars. We perform a spectroscopic analysis on a subsample of 84 DAs, and provide their atmospheric parameters. In particular, we identify 11 new white dwarfs with spectroscopic distances within 25pc of the Sun, including five candidates to the D<20pc subset.
