- ID:
- ivo://CDS.VizieR/J/AJ/126/3007
- Title:
- Spectroscopy of faint red NLTT dwarfs
- Short Name:
- J/AJ/126/3007
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present low-resolution optical spectroscopy and BVRI photometry of 453 candidate nearby stars drawn from the NLTT (<I/98>) proper-motion catalog. The stars were selected based on optical/near-infrared colors, derived by combining the NLTT photographic data with photometry from the 2MASS Second Incremental Data Release (<II/241>). Based on the derived photometric and spectroscopic parallaxes, we identify 111 stars as lying within 20pc of the Sun, including nine stars with formal distance estimates of less than 10pc. A further 53 stars have distance estimates within 1{sigma} of our 20pc limit. Almost all of those stars are additions to the nearby-star census. In total, our NLTT-based survey has so far identified 496 stars likely to be within 20pc, of which 195 are additions to nearby-star catalogs. Most of the newly identified nearby stars have spectral types between M4 and M8.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/132/1517
- Title:
- Spectroscopy of M dwarfs in Praesepe
- Short Name:
- J/AJ/132/1517
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopy of 222 late-type dwarfs in the Praesepe open cluster is used to measure the strengths of molecular and atomic features and to examine their sensitivity to chromospheric activity as measured by the strength of H{alpha} emission.
- ID:
- ivo://CDS.VizieR/J/AJ/123/2828
- Title:
- Spectroscopy of northern NLTT stars
- Short Name:
- J/AJ/123/2828
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present initial results of an all-sky search for late-type dwarfs within 20pc of the Sun using the New Luyten Two-Tenths (NLTT) catalog cross-referenced with the Two Micron All Sky Survey (2MASS) database. The results were obtained with low-resolution optical spectroscopic follow-up of candidate nearby stars as a preliminary test of our methodology. M_J_, derived using spectral indices, and 2MASS J are used to estimate distances. Out of the 70 objects observed, 28 are identified as previously unrecognized objects within 25pc of the Sun, and up to 19 of these are within 20pc. One, LP 647-13, is an M9-type dwarf at 10.5pc, making it one of the four closest M9 dwarfs currently known. We also discuss the chromospheric activity of the observed dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/546/A57
- Title:
- Spectroscopy of 400 red giants in the Bulge
- Short Name:
- J/A+A/546/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of two stellar populations in the Milky Way bulge has been reported recently, based on observations of giant and dwarf stars in the inner an intermediate bulge. We aim at studying the abundances and kinematics of stars in the outer Galactic bulge, thereby providing additional constraints on formation models of the bulge. Spectra of 401 red giant stars in a field at (l,b)=(0,-10) were obtained with the FLAMES-GIRAFFE spectrograph at the VLT. Stars of luminosities down to below the two bulge red clumps are included in the data set. From these spectra we measure general metallicities, abundances of iron and the alpha-elements, and radial velocities of the stars. The abundances are derived from an interpolation and fitting procedure within a grid of COMARCS model atmospheres and spectra. These measurements as well as photometric data are compared to simulations with the Besancon and TRILEGAL models of the Galaxy. We confirm the presence of two populations among our sample stars: i) a metal-rich one at [M/H]~+0.3, comprising about 30% of the sample, with low velocity dispersion and low alpha-abundance, and ii) a metal-poor population at [M/H]~-0.6 with high velocity dispersion and high alpha-abundance. The metallicity difference between the two populations, a systematically and statistically robust figure, is Delta[M/H]=0.87+-0.03. The metal-rich population could be connected to the Galactic bar. We identify this population as the carrier of the double red clump feature. We do not find a significant difference in metallicity or radial velocity between the two red clumps, a small difference in metallicity being probably due to a selection effect and contamination by the metal-poor population. The velocity dispersion agrees well with predictions of the Besancon Galaxy model, but the metallicity of the "thick bulge" model component should be shifted to lower metallicity by 0.2 to 0.3dex to well reproduce the observations. We present evidence that the metallicity distribution function depends on the evolutionary state of the sample stars, suggesting that enhanced mass loss preferentially removes metal-rich stars. We also confirm the decrease of alpha-element over-abundance with increasing metallicity. Conclusions: Our sample is consistent with the existence of two populations, one being a metal-rich bar, the second one being more like a metal-poor classical bulge with larger velocity dispersion.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/1323
- Title:
- Spectroscopy of stars in the Galaxy's nuclear cluster
- Short Name:
- J/ApJ/703/1323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the structure of the nuclear star cluster in the innermost 0.16pc of the Galaxy as measured by the number density profile of late-type giants. Using laser guide star adaptive optics in conjunction with the integral field spectrograph, OSIRIS, at the Keck II telescope, we are able to differentiate between the older, late-type (~1Gyr) stars, which are presumed to be dynamically relaxed, and the unrelaxed young (~6Myr) population. This distinction is crucial for testing models of stellar cusp formation in the vicinity of a black hole, as the models assume that the cusp stars are in dynamical equilibrium in the black hole potential. In the survey region, we classified 60 stars as early-type (O and early B; 22 newly identified) and 74 stars as late-type (K and M; 61 newly identified). We find that contamination from young stars is significant, with more than twice as many young stars as old stars in our sensitivity range (K'<15.5) within the central arcsecond.
- ID:
- ivo://CDS.VizieR/J/AJ/147/146
- Title:
- Spectroscopy of Tuc-Hor candidate members
- Short Name:
- J/AJ/147/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the selection and spectroscopic confirmation of 129 new late-type (SpT=K3-M6) members of the Tucana-Horologium moving group, a nearby (d~40pc), young ({tau}~40Myr) population of comoving stars. We also report observations for 13 of the 17 known Tuc-Hor members in this spectral type range, and that 62 additional candidates are likely to be unassociated field stars; the confirmation frequency for new candidates is therefore 129/191=67%. We have used radial velocities, H{alpha} emission, and Li_6708_ absorption to distinguish between contaminants and bona fide members. Our expanded census of Tuc-Hor increases the known population by a factor of ~3 in total and by a factor of ~8 for members with SpT>=K3, but even so, the K-M dwarf population of Tuc-Hor is still markedly incomplete. Our expanded census allows for a much more detailed study of Tuc-Hor than was previously feasible. The spatial distribution of members appears to trace a two-dimensional sheet, with a broad distribution in X and Y, but a very narrow distribution (+/-5pc) in Z. The corresponding velocity distribution is very small, with a scatter of +/-1.1km/s about the mean UVW velocity for stars spanning the entire 50pc extent of Tuc-Hor. We also show that the isochronal age ({tau}~20-30Myr) and the lithium depletion boundary age ({tau}~40Myr) disagree, following the trend in other pre-main-sequence populations for isochrones to yield systematically younger ages. The H{alpha} emission line strength follows a trend of increasing equivalent width with later spectral type, as is seen for young clusters. We find that moving group members have been depleted of measurable lithium for spectral types of K7.0-M4.5. None of our targets have significant infrared excesses in the WISE W3 band, yielding an upper limit on warm debris disks of F<0.7%. Finally, our purely kinematic and color-magnitude selection procedure allows us to test the efficiency and completeness for activity-based selection of young stars. We find that 60% of K-M dwarfs in Tuc-Hor do not have ROSAT counterparts and would have been omitted in X-ray-selected samples. In contrast, GALEX UV-selected samples using a previously suggested criterion for youth achieve completeness of 77% and purity of 78%, and we suggest new SpT-dependent selection criteria that will yield >95% completeness for {tau}~40Myr populations with GALEX data available.
- ID:
- ivo://CDS.VizieR/J/ApJ/710/1142
- Title:
- SpeX spectroscopy of low mass binaries. I.
- Short Name:
- J/ApJ/710/1142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the identification of 17 candidate brown dwarf binaries whose components straddle the L dwarf/T dwarf transition. These sources were culled from a large near-infrared spectral sample of L and T dwarfs observed with the Infrared Telescope Facility SpeX spectrograph. Candidates were selected on the basis of spectral ratios which segregate known (resolved) L dwarf/T dwarf pairs from presumably single sources. Composite templates, constructed by combining 13581 pairs of absolute flux-calibrated spectra, are shown to provide statistically superior fits to the spectra of our 17 candidates as compared to single templates. Ten of these candidates appear to have secondary components that are significantly brighter than their primaries over the 1.0-1.3um band, indicative of rapid condensate depletion at the L dwarf/T dwarf transition. Our results support prior indications of enhanced multiplicity amongst early-type T dwarfs; 53+/-7% of the T0-T4 dwarfs in our spectral sample are found to be either resolved or unresolved (candidate) pairs, although this is consistent with an intrinsic (volume complete) brown dwarf binary fraction of only 15%. If verified, this sample of spectral binaries more than doubles the number of known L dwarf/T dwarf transition pairs, enabling a broader exploration of this poorly understood phase of brown dwarf atmospheric evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/651/502
- Title:
- Spitzer IRAC photometry of M, L, and T dwarfs
- Short Name:
- J/ApJ/651/502
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/720
- Title:
- Spitzer observations of the Hyades
- Short Name:
- J/ApJ/679/720
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Spitzer Space Telescope to search for infrared excess at 24, 70, and 160um due to debris disks around a sample of 45 FGK-type members of the Hyades. We supplement our observations with archival 24 and 70um Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members in order to provide robust statistics on the incidence of debris disks at 625Myr of age, an era corresponding to the late heavy bombardment in the solar system. We find that none of the 67 FGK-type stars in our sample show evidence for a debris disk, while 2 out of the 11 A-type stars do. This difference in debris disk detection rate is likely to be due to a sensitivity bias in favor of early-type stars. The fractional disk luminosity, L_dust_/L_*_, of the disks around the two A-type stars is ~4x10^-5^, a level that is below the sensitivity of our observations toward the FGK-type stars. However, our sensitivity limits for FGK-type stars are able to exclude, at the 2{sigma} level, frequencies higher than 12% and 5% of disks with L_dust_/L_*_>1x10^-4^ and L_dust_/L_*_>5x10^-4^, respectively. We also use our sensitivity limits and debris disk models to constrain the maximum mass of dust, as a function of distance from the stars, that could remain undetected around our targets.
- ID:
- ivo://CDS.VizieR/J/A+A/517/A44
- Title:
- Spitzer sources in the Galactic bulge
- Short Name:
- J/A+A/517/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric catalogue of seven selected fields towards the Galactic bulge, observed with the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope with unprecedented sensitivity. The locations of the fields are defined in Figure 1 and Table 1 of the paper. In each of the fields, tens of thousands of point sources were detected. The catalogue is split up into seven tables, according to the different fields. Table 5 in the paper gives ten lines of the band-merged catalogue of the Bulge N1 field as an example. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue. Besides a catalogue for each field, fits files of the IRAC and MIPS mosaics are presented, too. As a cautionary note for the users, we would like to add that the least reliable sources in our catalogue are those with detection in only one IRAC band and no MIPS detection, and with (i) either no 2MASS and DENIS counterpart (depending on the field, between 3.1% and 6.7% of the sources), or (ii) a DENIS and 2MASS counterpart at a distance between 1.6 and 3 arcseconds (depending on the field, between 0.4% and 1.0% of the sources).
