- 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}_).
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Search Results
- 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/AJ/154/14
- Title:
- Low-mass stars in 25 Ori group and Orion OB1a
- Short Name:
- J/AJ/154/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion OB1a sub-association is a rich low-mass star (LMS) region. Previous spectroscopic studies have confirmed 160 LMSs in the 25 Orionis stellar group (25 Ori), which is the most prominent overdensity of Orion OB1a. Nonetheless, the current census of the 25 Ori members is estimated to be lower than 50% complete, leaving a large number of members to be still confirmed. We retrieved 172 low-resolution stellar spectra in Orion OB1a observed as ancillary science in the SDSS-III/BOSS survey, for which we classified their spectral types and determined physical parameters. To determine memberships, we analyzed the H{alpha} emission, LiI{lambda}6708 absorption, and NaI{lambda}{lambda}8183,8195 absorption as youth indicators in stars classified as M type. We report 50 new LMSs spread across the 25 Orionis, ASCC18, and ASCC20 stellar groups with spectral types from M0 to M6, corresponding to a mass range of 0.10{<=}m/M_{Sun}_{<=}0.58. This represents an increase of 50% in the number of known LMSs in the area and a net increase of 20% in the number of 25 Ori members in this mass range. Using parallax values from the Gaia DR1 catalog, we estimated the distances to these three stellar groups and found that they are all co-distant, at 338+/-66pc. We analyzed the spectral energy distributions of these LMSs and classified their disks into evolutionary classes. Using H-R diagrams, we found a suggestion that 25 Ori could be slightly older than the other two observed groups in Orion OB1a.
- ID:
- ivo://CDS.VizieR/J/AJ/128/805
- Title:
- Low-mass stars in the Cepheus OB2 region
- Short Name:
- J/AJ/128/805
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first identification of low-mass (spectral types K-M) stars in the young clusters Tr37 and NGC7160, members of the CepOB2 association. This is part of a program to follow the evolution of protoplanetary accretion disks through the ages thought to be crucial to understanding disk dissipation and planet formation (~3-10Myr). Combining optical photometry and optical spectroscopy, we have identified ~40 members in Tr37 and ~15 in NGC7160, using several independent tests for determining the membership (optical colors, optical variability, H{alpha} emission, and Li{lambda}6707 absorption).
- ID:
- ivo://CDS.VizieR/J/MNRAS/423/2966
- Title:
- Low-mass stars spectroscopy in NGC 2516
- Short Name:
- J/MNRAS/423/2966
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present far-red, intermediate-resolution spectroscopy of 572 photometrically selected, low-mass stars (0.2<M/M_{sun}_<0.7) in the young open cluster NGC 2516, using the FLAMES spectrograph at the Very Large Telescope. Precise radial velocities confirm membership for 210 stars that have published rotation periods from spot-modulated light curves and for another 144 stars in which periodic modulation could not be found. The two subsamples are compared and no significant differences are found between their positions in colour-magnitude diagrams, the distribution of their projected equatorial velocities or their levels of chromospheric activity.
- ID:
- ivo://CDS.VizieR/J/ApJ/711/928
- Title:
- Low-redshift Ly{alpha} galaxies from GALEX
- Short Name:
- J/ApJ/711/928
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a sample of low-redshift Ly{alpha} emission-line selected sources from Galaxy Evolution Explorer (GALEX) grism spectroscopy of nine deep fields to study the role of Ly{alpha} emission in galaxy populations with cosmic time. Our final sample consists of 119 (141) sources selected in the redshift interval z=0.195-0.44 (z=0.65-1.25) from the FUV (NUV) channel. We classify the Ly{alpha} sources as active galactic nuclei (AGNs) if high-ionization emission lines are present in their UV spectra and as possible star-forming galaxies otherwise. We classify additional sources as AGNs using line widths for our Ly{alpha} emitter (LAE) analysis. These classifications are broadly supported by comparisons with X-ray and optical spectroscopic observations, though the optical spectroscopy identifies a small number of additional AGNs. Defining the GALEX LAE sample in the same way as high-redshift LAE samples, we show that LAEs constitute only about 5% of NUV-continuum selected galaxies at z~0.3. We also show that they are less common at z~0.3 than they are at z~3. Finally, we confirm that the z~2 Lyman break galaxies have relatively low metallicities for their luminosities, and we find that they lie in the same metallicity range as the z~0.3 Ly{alpha} galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/194
- Title:
- Low-z intergalactic medium. III.
- Short Name:
- J/ApJ/679/194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conduct an ultraviolet (HST and FUSE) spectroscopic survey of HI (Lyman lines) and seven metal ions (OVI, NV, CIV, CIII, SiIV, SiIII, FeIII) in the low-redshift IGM at z<0.4. We analyzed 650 Ly{alpha} absorbers over redshift path length {Delta}z=5.27, detecting numerous absorbers: 83 OVI systems, 39 CIII, 53 SiIII, 24 CIV, 24 NV, and so on. In the low-z IGM, we have accounted for ~40% of the baryons: 30% in the photoionized Ly{alpha} forest and 10% in the (T=10^5^-10^6^) WHIM traced by OVI. Statistical metallicities are consistent with the canonical value of 10% solar, with considerable scatter.
- ID:
- ivo://CDS.VizieR/J/A+A/599/A76
- Title:
- L-{sigma} relation for HII galaxies
- Short Name:
- J/A+A/599/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The correlation between emission-line luminosity (L) and profile-width ({sigma}) for HII galaxies provides a powerful method to measure the distances to galaxies over a wide range of redshifts. In this paper, we use SDSS spectrophotometry to explore the systematics of the correlation using the [OIII]5007 lines instead of H{alpha} or H{beta} to measure luminosities and line widths. We also examine possible systematic effects involved in measuring the profile-widths and the luminosities through different apertures. We find that the green L-{sigma} relation, defined using [OIII]5007 luminosities, is significantly more sensitive than H{beta} to the effects of age and the physical conditions of the nebulae, which more than offsets the advantage of the higher strength of the [OIII]5007 lines. We then explore the possibility of mixing [OIII]5007 profile-widths with SDSS H{beta} luminosities using the Hubble constant H_0_ to quantify the possible systematic effects. We find the mixed L(H{beta})-{sigma}_[OIII]_ relation to be at least as powerful as the canonical L-{sigma} relation as a distance estimator, and we show that evolutionary corrections do not change the slope and the scatter of the correlation and, therefore, do not bias the L-{sigma} distance indicator at high redshifts. Locally, however, the luminosities of the giant HII regions that provide the zero-point calibrators are sensitive to evolutionary corrections and may bias the Hubble constant if their mean ages, as measured by the equivalent widths of H{beta}, are significantly different from the mean age of the HII galaxies. Using a small sample of 16 ad-hoc zero point calibrators we obtain a value of H_0_=66.4^+5.0^_-4.5_km/s/Mpc for the Hubble constant, which is fully consistent with the best modern determinations, and which is not biased by evolutionary corrections.
