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17951. Yellow supergiants in the SMC
ID:
ivo://CDS.VizieR/J/ApJ/719/1784
Title:
Yellow supergiants in the SMC
Short Name:
J/ApJ/719/1784
Date:
21 Oct 2021
Publisher:
CDS
Description:
The yellow supergiant content of nearby galaxies provides a critical test of massive star evolutionary theory. While these stars are the brightest in a galaxy, they are difficult to identify because a large number of foreground Milky Way stars have similar colors and magnitudes. We previously conducted a census of yellow supergiants within M31 and found that the evolutionary tracks predict a yellow supergiant duration an order of magnitude longer than we observed. Here we turn our attention to the Small Magellanic Cloud (SMC), where the metallicity is 10x lower than that of M31, which is important as metallicity strongly affects massive star evolution. The SMC's large radial velocity (~160km/s) allows us to separate members from foreground stars. Observations of ~500 candidates yielded 176 near-certain SMC supergiants, 16 possible SMC supergiants, along with 306 foreground stars, and provide good relative numbers of yellow supergiants down to 12M_{sun}_. Of the 176 near-certain SMC supergiants, the kinematics predicted by the Besancon model of the Milky Way suggest a foreground contamination of <=4%. After placing the SMC supergiants on the Hertzsprung-Russell diagram (HRD) and comparing our results to the Geneva evolutionary tracks, we find results similar to those of the M31 study: while the locations of the stars on the HRD match the locations of evolutionary tracks well, the models overpredict the yellow supergiant lifetime by a factor of 10. Uncertainties about the mass-loss rates on the main sequence thus cannot be the primary problem with the models.
17952. YJK for Type Ia supernovae
ID:
ivo://CDS.VizieR/J/MNRAS/448/1345
Title:
YJK for Type Ia supernovae
Short Name:
J/MNRAS/448/1345
Date:
21 Oct 2021
Publisher:
CDS
Description:
Type Ia supernovae (SNe Ia) have been proposed to be much better distance indicators at near-infrared (NIR) compared to optical wavelengths - the effect of dust extinction is expected to be lower and it has been shown that SNe Ia behave more like `standard candles' at NIR wavelengths. To better understand the physical processes behind this increased uniformity, we have studied the Y, J and H-filter light curves of 91 SNe Ia from the literature. We show that the phases and luminosities of the first maximum in the NIR light curves are extremely uniform for our sample. The phase of the second maximum, the late-phase NIR luminosity and the optical light-curve shape are found to be strongly correlated, in particular more luminous SNe Ia reach the second maximum in the NIR filters at a later phase compared to fainter objects. We also find a strong correlation between the phase of the second maximum and the epoch at which the SN enters the Lira law phase in its optical colour curve (epochs ~15 to 30d after B-band maximum). The decline rate after the second maximum is very uniform in all NIR filters. We suggest that these observational parameters are linked to the nickel and iron mass in the explosion, providing evidence that the amount of nickel synthesized in the explosion is the dominating factor shaping the optical and NIR appearance of SNe Ia.
17953. YMGs. I. Young binaries & lithium-rich stars
ID:
ivo://CDS.VizieR/J/ApJ/877/60
Title:
YMGs. I. Young binaries & lithium-rich stars
Short Name:
J/ApJ/877/60
Date:
21 Oct 2021
Publisher:
CDS
Description:
Young stars in the solar neighborhood serve as nearby probes of stellar evolution and represent promising targets to directly image self-luminous giant planets. We have carried out an all-sky search for late-type (~K7-M5) stars within 100pc selected primarily on the basis of activity indicators from the Galaxy Evolution Explorer and ROSAT. Approximately 2000 active and potentially young stars are identified, of which we have followed up over 600 with low-resolution optical spectroscopy and over 1000 with diffraction-limited imaging using Robo-AO at the Palomar 1.5m telescope. Strong lithium is present in 58 stars, implying ages spanning ~10-200Myr. Most of these lithium-rich stars are new or previously known members of young moving groups including TWA, {beta}Pic, Tuc-Hor, Carina, Columba, Argus, ABDor, Upper Centaurus Lupus, and Lower Centaurus Crux; the rest appear to be young low-mass stars without connections to established kinematic groups. Over 200 close binaries are identified down to 0.2"-the vast majority of which are new-and will be valuable for dynamical mass measurements of young stars with continued orbit monitoring in the future.
17954. 12Y-MST and 12Y-MSTw Catalogues
ID:
ivo://CDS.VizieR/J/A+A/652/A6
Title:
12Y-MST and 12Y-MSTw Catalogues
Short Name:
J/A+A/652/A6
Date:
22 Feb 2022
Publisher:
CDS
Description:
We present an updated version catalogue of gamma-ray source candidates, 12Y-MST, selected using the Minimum Spanning Tree (MST) algorithm on the 12-years Fermi/LAT sky (Pass 8) at energies higher than 10GeV. The high energy sky at absolute Galactic latitudes above 20 degrees has been investigated using rather restrictive selection criteria, resulting in a total sample of 1664 photon clusters, or candidate sources. Of these, 230 are new detections, i.e., candidate sources without any association in other gamma-ray catalogues. A large fraction of them have interesting counterparts, most likely blazars. In this paper the main results on the catalogue selection and search of counterparts are described. We also present an additional sample of 224 candidate sources (12Y-MSTw), which are clusters extracted applying weaker selection criteria: about 57% of them have not been reported in other catalogues.
17955. 9Y-MST Catalogue
ID:
ivo://CDS.VizieR/J/A+A/619/A23
Title:
9Y-MST Catalogue
Short Name:
J/A+A/619/A23
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe a catalogue of gamma-ray source candidates selected using the minimum spanning tree (MST) algorithm on the nine year Fermi-LAT sky (Pass 8) at energies higher than 10GeV. The extragalactic sky at absolute Galactic latitudes above 20{deg} has been investigated using rather restrictive selection criteria, resulting in a total sample of 1342 sources. Of these, 249 are new detections that have not been previously associated with gamma-ray catalogues. A large portion of these candidates have interesting counterparts, which are most likely blazars. In this paper, we report the main results of the catalogue selection and search of counterparts.
17956. Young and embedded clusters in Cygnus-X
ID:
ivo://CDS.VizieR/J/MNRAS/458/3027
Title:
Young and embedded clusters in Cygnus-X
Short Name:
J/MNRAS/458/3027
Date:
21 Oct 2021
Publisher:
CDS
Description:
We provide a new view on the Cygnus-X north complex by accessing for the first time the low mass content of young stellar populations in the region. CFHT/WIRCam camera was used to perform a deep near-IR survey of this complex, sampling stellar masses down to ~0.1M_{sun}_. Several analysis tools, including a extinction treatment developed in this work, were employed to identify and uniformly characterise a dozen unstudied young star clusters in the area. Investigation of their mass distributions in low-mass domain revealed a relatively uniform log-normal IMF with a characteristic mass of 0.32+/-0.08M_{sun}_ and mass dispersion of 0.40+/-0.06. In the high mass regime, their derived slopes showed that while the youngest clusters (age<4Myr) presented slightly shallower values with respect to the Salpeter's, our older clusters (4Myr<age<18Myr) showed IMF compliant values and a slightly denser stellar population. Although possibly evidencing a deviation from an 'universal' IMF, these results also supports a scenario where these gas dominated young clusters gradually 'build up' their IMF by accreting low-mass stars formed in their vicinity during their first ~3Myr, before the gas expulsion phase, emerging at the age of ~4Myr with a fully fledged IMF. Finally, the derived distances to these clusters confirmed the existence of at least 3 different star forming regions throughout Cygnus-X north complex, at distances of 500-900pc, 1.4-1.7kpc and 3.0kpc, and revealed evidence of a possible interaction between some of these stellar populations and the Cygnus-OB2 association.
17957. Young binaries in Ophiuchus&Upper Centaurus-Lupus
ID:
ivo://CDS.VizieR/J/AJ/155/109
Title:
Young binaries in Ophiuchus&Upper Centaurus-Lupus
Short Name:
J/AJ/155/109
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present measurements of the orbital positions and flux ratios of 17 binary and triple systems in the Ophiuchus star-forming region and the Upper Centaurus-Lupus cluster based on adaptive optics imaging at the Keck Observatory. We report the detection of visual companions in MML 50 and MML 53 for the first time, as well as the possible detection of a third component in WSB 21. For six systems in our sample, our measurements provide a second orbital position following their initial discoveries over a decade ago. For eight systems with sufficient orbital coverage, we analyze the range of orbital solutions that fit the data. Ultimately, these observations will help provide the groundwork toward measuring precise masses for these pre-main-sequence stars and understanding the distribution of orbital parameters in young multiple systems.
17958. 13 young brown dwarfs SINFONI spectra
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.
17959. Young clumps embedded in IRDC
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}_.
17960. Young companion candidate embedded in R CrA cloud
ID:
ivo://CDS.VizieR/J/A+A/624/A29
Title:
Young companion candidate embedded in R CrA cloud
Short Name:
J/A+A/624/A29
Date:
21 Oct 2021
Publisher:
CDS
Description:
Within the NaCo-ISPY exoplanet imaging program, we aim at detecting and characterizing the population of low-mass companions at wide separations (>~10AU). We observed R CrA twice with the NaCo instrument at the Very Large Telescope (VLT) in the L' filter with a one year time baseline in between. We used artificial negative signals to determine the position and brightness of the companion and the related uncertainties. The companion is detected at a separation of 196.8+/-4.5/196.6+/-5.9mas (18.7+/-1.3/18.7+/-1.4AU) and position angle of 134.7+/-0.5{deg}/133.7+/-0.7{deg} in the first/second epoch observation. We measure a contrast of 7.29+/-0.18/6.70+/-0.15mag with respect to the primary. A study of the stellar proper motion rejects the hypothesis that the signal is a background object. Depending on the assumed age, extinction, and brightness of the primary, the stellar companion has a mass between 0.10+/-0.02M_{sun}_ and 1.03^+0.20^_-0.18_M_{sun}_ range, if no contribution from circumsecondary material is taken into account. The presence of this companion needs to be taken into account when analyzing the complex circumstellar environment of R CrA.

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