- ID:
- ivo://CDS.VizieR/J/ApJ/838/73
- Title:
- Brown dwarf surface gravities with Keck/NIRSPEC
- Short Name:
- J/ApJ/838/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combine 131 new medium-resolution (R~2000) J-band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5-T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6-L7 objects in our sample by measuring the equivalent widths (EW) of the K I lines at 1.1692, 1.1778, and 1.2529{mu}m, and the 1.2{mu}m FeH_J_ absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak-at ~L5 and T5-in K I EW as a function of spectral type. We analyze the K I EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6-L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.
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- ID:
- ivo://CDS.VizieR/J/ApJ/842/118
- Title:
- Brown dwarfs with spectral type later than T6
- Short Name:
- J/ApJ/842/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The survey of the mid-infrared sky by the Wide-field Infrared Survey Explorer (WISE) led to the discovery of extremely cold, low-mass brown dwarfs, classified as Y dwarfs, which extend the T class to lower temperatures. Twenty-four Y dwarfs are known at the time of writing. Here we present improved parallaxes for four of these, determined using Spitzer images. We give new photometry for four late-type T and three Y dwarfs and new spectra of three Y dwarfs, obtained at Gemini Observatory. We also present previously unpublished photometry taken from HST, ESO, Spitzer, and WISE archives of 11 late-type T and 9 Y dwarfs. The near-infrared data are put onto the same photometric system, forming a homogeneous data set for the coolest brown dwarfs. We compare recent models to our photometric and spectroscopic data set. We confirm that nonequilibrium atmospheric chemistry is important for these objects. Nonequilibrium cloud-free models reproduce well the near-infrared spectra and mid-infrared photometry for the warmer Y dwarfs with 425<=T_eff_(K)<=450. A small amount of cloud cover may improve the model fits in the near-infrared for the Y dwarfs with 325<=T_eff_(K)<=375. Neither cloudy nor cloud-free models reproduce the near-infrared photometry for the T_eff_=250K Y dwarf WISEJ085510.83-071442.5 (W0855). We use the mid-infrared region, where most of the flux originates, to constrain our models of W0855. We find that W0855 likely has a mass of 1.5-8 Jupiter masses and an age of 0.3-6Gyr. The Y dwarfs with measured parallaxes are within 20pc of the Sun and have tangential velocities typical of the thin disk. The metallicities and ages we derive for the sample are generally solar-like. We estimate that the known Y dwarfs are 3 to 20 Jupiter-mass objects with ages of 0.6-8.5Gyr.
- ID:
- ivo://CDS.VizieR/J/A+A/454/453
- Title:
- BR photometry and redshifts of IDS galaxies
- Short Name:
- J/A+A/454/453
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The IRAS Deep Survey (IDS) of the North Ecliptic Pole region remains one of the deepest complete far-infrared-selected galaxy samples available. ISOCAM observations in the LW3 filter (12-18{mu}m) of 3.2'x3.2' fields centered on the nominal positions of 94 out of the 98 IDS sources yielding 116 ISOCAM detections. The resulting sample has allowed us to assess the source reliability, identify confusion effects, and pinpoint optical counterparts. To fully exploit the potential of this sample for investigating galaxy evolution, we carried out optical observations of candidate identifications to 100 out of the 116 ISOCAM sources. Optical imaging was acquired for 88 galaxies in 54 IDS fields: 44 galaxies were imaged in both the B- and the R-band, 33 only in the R-band, and 11 only in the B-band. These observations aimed at extending the MIR/FIR spectral energy distribution to the optical region and achieving morphological information. In addition, spectra were obtained for 65 IDS fields, 20 of which had not been observed before. Redshifts were measured for the 85 galaxies found within the positional error circles of 77 ISOCAM sources detected in those IDS fields.
- ID:
- ivo://CDS.VizieR/J/AJ/117/75
- Title:
- BR photometry in Coma, A2199 & AWM5 clusters
- Short Name:
- J/AJ/117/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study on galaxy interactions, tides, and other processes that produce luminous fine-scale substructures in the galaxy clusters: Coma, Perseus, Abell 2199, AWM 3, and AWM 5. All unusual structures in these clusters can be categorized into seven morphologies: interacting galaxies, multiple galaxies (noninteracting), distorted galaxies, tailed galaxies, line galaxies, dwarf galaxy groups, and galaxy aggregates. The various morphologies are described, and a catalog is presented, of 248 objects in these five clusters along with color, and positional information obtained from CCD images taken with the WIYN 3.5 m telescope in broadband B and R filters.
- ID:
- ivo://CDS.VizieR/J/A+A/363/440
- Title:
- BR photometry of Abell 2104
- Short Name:
- J/A+A/363/440
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The cluster Abell 2104 is one of the lowest redshift clusters (z=0.153) known to have a gravitational lensing arc. We present detailed analysis of the cluster properties such as the gravitational potential using the X-ray data from ROSAT (HRI) and ASCA, as well as optical imaging and spectroscopic data from the CFHT.
- ID:
- ivo://CDS.VizieR/J/MNRAS/287/293
- Title:
- BR photometry of EUVE sources
- Short Name:
- J/MNRAS/287/293
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most of the sources detected in the extreme ultraviolet (EUV; 100-600{AA}) by the ROSAT/WFC and EUVE all-sky surveys have been identified with active late-type stars and hot white dwarfs that are near enough to the Earth to escape absorption by interstellar gas. However, about 15 per cent of EUV sources are as yet unidentified with any optical counterparts. We examine whether the unidentified EUV sources may consist of the same population of late-type stars and white dwarfs. We present B and R photometry of stars in the fields of seven of the unidentified EUV sources. We detect in the optical the entire main-sequence and white dwarf population out to the greatest distances where they could still avoid absorption. We use colour-magnitude diagrams to demonstrate that, in most of the fields, none of the observed stars has the colours and magnitudes of late-type dwarfs at distances less than 100pc. Similarly, none of the observed stars is a white dwarf within 500pc that is hot enough to be a EUV emitter. The unidentified EUV sources we study are not detected in X-rays, while cataclysmic variables, X-ray binaries, and active galactic nuclei generally are. We conclude that some of the EUV sources may be a new class of nearby objects, which are either very faint at optical bands or which mimic the colours and magnitudes of distant late-type stars or cool white dwarfs. One candidate for optically faint objects is isolated old neutron stars, slowly accreting interstellar matter. Such neutron stars are expected to be abundant in the Galaxy, and have not been unambiguously detected.
- ID:
- ivo://CDS.VizieR/J/PASP/110/533
- Title:
- BR photometry of Fornax bright stars
- Short Name:
- J/PASP/110/533
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present accurate photometry on the Johnson B, Kron-Cousins R photometric system for approximately 100,000 stars in a 1/3deg^2^ field centered on the dwarf spheroidal galaxy in Fornax. We identify numerous probable short-period variable stars, blue stars that appear to be the main sequence of a small population with an age of order 108yr, and two distinct types of luminous red star: an extended sequence of primarily carbon stars and a clump of mostly M giants slightly more luminous than the giant-branch tip. The spatial distribution of each of these subpopulations within the Fornax dwarf galaxy is considered.
- ID:
- ivo://CDS.VizieR/J/AJ/131/912
- Title:
- BR photometry of Fornax dSph center
- Short Name:
- J/AJ/131/912
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have imaged the recently discovered stellar overdensity located approximately one core radius from the center of the Fornax dwarf spheroidal galaxy using the Magellan Clay 6.5m telescope with the Magellan Instant Camera. Superb seeing conditions allowed us to probe the stellar populations of this overdensity and of a control field within Fornax to a limiting magnitude of R=26. The color-magnitude diagram of the overdensity field is virtually identical to that of the control field, with the exception of the presence of a population arising from a very short (less than 300Myr in duration) burst of star formation 1.4Gyr ago.
- ID:
- ivo://CDS.VizieR/J/A+AS/117/261
- Title:
- BR photometry of galaxies in low density regions
- Short Name:
- J/A+AS/117/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform detailed surface photometry, based on B- and/or R-band CCD images of 92 faint galaxies. They are a subsample of those galaxies which were studied by Hopp et al. (1994) in the direction of three nearby voids. We derive integral photometric parameters and radial surface brightness profiles and compare them to those of several faint galaxy samples, located in different environments, and of a bright field galaxy sample. According to the obtained photometric characteristics, our sample is a mixture of intrinsically bright and faint galaxies, about 60% of them belonging to the bright subsample (M_B_<-19.0). These bright ones show mean characteristics of typical Freeman's disks and are mainly located in the background of the observed voids. The faint subsample (M_B_>=-19.0) has parameters typical for the low-surface-brightness (LSB) galaxies. There are a few well isolated galaxies both among the bright and faint subsamples.
- ID:
- ivo://CDS.VizieR/J/A+A/433/751
- Title:
- BR photometry of nearby Southern dwarf galaxies
- Short Name:
- J/A+A/433/751
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out CCD photometry in the Johnson-Cousins B and R bands of 23 dwarf galaxies: SDIG, ESO 410-17, KK11, ESO 245-05, KKs3, KK27, KK38, KK40, IC 4662, KK244, KK246, KK247, KK248, KK249, KK253, KK255, KK256, KK257, KK258, KK259, UGCA 438, ESO 347-17, and UGCA 442. Both isolated galaxies and members of the Sculptor group and the NGC 1313 group were observed. The galaxy sample is characterized by a median distance of 9.3Mpc, and median absolute magnitude of -14.8mag. The central surface brightnesses are in the range from 22.2 to 24.4mag/arcsec^2^ in B.
