- ID:
- ivo://CDS.VizieR/J/AJ/133/394
- Title:
- Low-mass binary companions in M35
- Short Name:
- J/AJ/133/394
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Space Telescope Fine Guidance Sensors data on 23 stars in the intermediate-age cluster M35 having B-V<0.5 (~F7V) are analyzed to test whether binary periods, separations, and masses can be estimated by measuring periodic variations in the residuals of their internal proper motions. Of the 23 stars examined, 4 appear to possess a periodic signal. Unfortunately, these detections cannot be considered firm because the amplitudes of these waveforms are small (~1mas), the signal is only seen in one coordinate, and the derived periods are close to the duration of the data set. If the signals are real, they predict binary separations of >6AU, secondary masses between 0.3 and 0.6M_{sun}_, and mass ratios of about 0.2. This latter value is in agreement with capture models employing stars with circumstellar disks for the formation of binaries.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/755/167
- Title:
- Low-mass black holes in SDSS Seyfert 1 galaxies
- Short Name:
- J/ApJ/755/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad H{alpha} emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN-galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range 8x10^4^-2x10^6^M_{sun}_ (with a median of 1.2x10^6^M_{sun}_), using the virial mass estimator based on the broad H{alpha} line. About half of our sample of low-mass BHs differs from that of Greene & Ho (2007, Cat. J/ApJ/670/92), with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from <~0.01 to ~1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of L* field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1Gyr.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/40
- Title:
- Low-mass black holes in Sy1 galaxies. II. SDSS-DR7
- Short Name:
- J/ApJS/235/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new sample of 204 low-mass black holes (LMBHs) in active galactic nuclei (AGNs) is presented with black hole masses in the range of (1-20)x10^5^M_{sun}_. The AGNs are selected through a systematic search among galaxies in the Seventh Data Release (DR7) of the Sloan Digital Sky Survey (SDSS), and careful analyses of their optical spectra and precise measurement of spectral parameters. Combining them with our previous sample selected from SDSS DR4 makes it the largest LMBH sample so far, totaling over 500 objects. Some of the statistical properties of the combined LMBH AGN sample are briefly discussed in the context of exploring the low-mass end of the AGN population. Their X-ray luminosities follow the extension of the previously known correlation with the [OIII] luminosity. The effective optical-to-X-ray spectral indices {alpha}_OX_, albeit with a large scatter, are broadly consistent with the extension of the relation with the near-UV luminosity L_2500{AA}_. Interestingly, a correlation of {alpha}_OX_ with black hole mass is also found, with {alpha}OX being statistically flatter (stronger X-ray relative to optical) for lower black hole masses. Only 26 objects, mostly radio loud, were detected in radio at 20cm in the FIRST survey, giving a radio-loud fraction of 4%. The host galaxies of LMBHs have stellar masses in the range of 10^8.8^-10^12.4^M_{sun}_ and optical colors typical of Sbc spirals. They are dominated by young stellar populations that seem to have undergone continuous star formation history.
- ID:
- ivo://CDS.VizieR/J/AJ/155/23
- Title:
- Low-mass fast rotators in the solar neighborhood
- Short Name:
- J/AJ/155/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The K2 mission is targeting large numbers of nearby (d<100 pc) GKM dwarfs selected from the SUPERBLINK proper motion survey ({mu}>40 mas/yr, V<20). Additionally, the mission is targeting low-mass, high proper motion stars associated with the local (d<500 pc) Galactic halo population also selected from SUPERBLINK. K2 campaigns 0 through 8 monitored a total of 26518 of these cool main-sequence stars. We used the auto-correlation function to search for fast rotators by identifying short-period photometric modulations in the K2 light curves. We identified 481 candidate fast rotators with rotation periods <4 days that show light-curve modulations consistent with starspots. Their kinematics show low average transverse velocities, suggesting that they are part of the young disk population. A subset (13) of the fast rotators is found among those targets with colors and kinematics consistent with the local Galactic halo population and may represent stars spun up by tidal interactions in close binary systems. We further demonstrate that the M dwarf fast rotators selected from the K2 light curves are significantly more likely to have UV excess and discuss the potential of the K2 mission to identify new nearby young GKM dwarfs on the basis of their fast rotation rates. Finally, we discuss the possible use of local halo stars as fiducial, non-variable sources in the Kepler fields.
- ID:
- ivo://CDS.VizieR/J/ApJ/684/654
- Title:
- Low-mass members of Chamaeleon I
- Short Name:
- J/ApJ/684/654
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used images obtained with the Infrared Array Camera and the Multiband Imaging Photometer on board the Spitzer Space Telescope to search for low-mass stars and brown dwarfs with circumstellar disks in the Chamaeleon I star-forming region. Through optical spectroscopy of sources with red colors in these data, we have identified seven new disk-bearing members of the cluster. Three of these objects are probably brown dwarfs, according to their spectral types (M8, M8.5, M8-L0). Three of the other new members may have edge-on disks, based on the shapes of their infrared spectral energy distributions. One of the possible edge-on systems has a steeply rising slope from 4.5 to 24um, indicating that it could be a Class I source (star+disk+envelope) rather than a Class II source (star+disk). If so, then it would be one of the least massive known Class I protostars (M5.75, M~0.1M_{sun}_).
- ID:
- ivo://CDS.VizieR/J/ApJS/134/103
- Title:
- Low-mass members of IC 2391
- Short Name:
- J/ApJS/134/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified a large sample of probable low-mass members of the young open cluster IC 2391 based on optical (VRIZ) and infrared (JHKs) photometry. Our sample includes 50 probable members and 82 possible members, both very low-mass stars and brown dwarfs. We also provide accurate positions for these stars and brown dwarf candidates derived from red UK Schmidt plates measured using the microdensitometer SuperCOSMOS. Assuming an age of 53Myr, we estimate that we have reached a mass of 0.025M_{sun}_, if the identified objects are indeed members of IC 2391.
- ID:
- ivo://CDS.VizieR/J/AJ/131/3016
- Title:
- Low-mass objects in Upper Scorpius
- Short Name:
- J/AJ/131/3016
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a wide-field photometric survey covering ~200^{deg}^2 toward the Upper Scorpius OB association. Data taken in the R and I bands with the Quest-2 camera on the Palomar 48inch (1.2m) telescope were combined with the Two Micron All Sky Survey JHK_S_ survey and used to select candidate pre-main-sequence stars. Follow-up spectroscopy with the Palomar 200inch (5.1m) telescope of 62 candidate late-type members identified 43 stars that have surface gravity signatures consistent with association membership.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/377
- Title:
- Low-mass objects in Upper Scorpius. II.
- Short Name:
- J/ApJ/688/377
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present continued results from a wide-field, ~150{deg}^2^, optical photometric and spectroscopic survey of the northern part of the ~5Myr old Upper Scorpius OB association. Photometry and spectral types were used to derive effective temperatures and luminosities and place newly identified association members onto a theoretical Hertzsprung-Russell diagram. From our survey, we have discovered 145 new low-mass members of the association and determined ~10% of these objects to be actively accreting material from a surrounding circumstellar disk.
- ID:
- ivo://CDS.VizieR/J/ApJ/752/59
- Title:
- Low-mass population in L1641
- Short Name:
- J/ApJ/752/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an optical photometric and spectroscopic survey of the young stellar population in L1641, the low-density star-forming region of the Orion A cloud south of the Orion Nebula Cluster (ONC). Our goal is to determine whether L1641 has a large enough low-mass population to make the known lack of high-mass stars a statistically significant demonstration of environmental dependence of the upper mass stellar initial mass function (IMF). Our spectroscopic sample consists of IR-excess objects selected from the Spitzer/IRAC survey and non-excess objects selected from optical photometry. We have spectral confirmation of 864 members, with another 98 probable members; of the confirmed members, 406 have infrared excesses and 458 do not. Assuming the same ratio of stars with and without IR excesses in the highly extincted regions, L1641 may contain as many as ~1600 stars down to ~0.1M_{sun}_, comparable within a factor of two to the ONC. Compared to the standard models of the IMF, L1641 is deficient in O and early B stars to a 3{sigma}-4{sigma} significance level, assuming that we know of all the massive stars in L1641.
- ID:
- ivo://CDS.VizieR/J/A+A/515/A75
- Title:
- Low-mass population in {rho} Oph cloud
- Short Name:
- J/A+A/515/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star formation theories are currently divergent regarding the fundamental physical processes that dominate the substellar regime. Observations of nearby young open clusters allow the brown dwarf (BD) population to be characterised down to the planetary mass regime, which ultimately must be accommodated by a successful theory. We used near-IR deep images (reaching completeness limits of approximately 20.5mag in J, and 18.9mag in H and Ks taken with the Wide Field IR Camera (WIRCam) at the Canada France Hawaii Telescope (CFHT) to identify candidate members of {rho} Oph in the substellar regime. A spectroscopic follow-up of a small sample of the candidates allows us to assess their spectral type, and subsequently their temperature and membership. We select 110 candidate members of the {rho} Ophiuchi molecular cloud, from which 80 have not previously been associated with the cloud. We observed a small sample of these and spectroscopically confirm six new brown dwarfs with spectral types ranging from M6.5 to M8.25.
