- ID:
- ivo://CDS.VizieR/J/AJ/159/257
- Title:
- Hawaii IR parallax program. IV. L0-T8 BDs with UKIRT
- Short Name:
- J/AJ/159/257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present parallaxes, proper motions, and J-band photometry for 348 L and T dwarfs measured using the wide-field near-infrared camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT). This is the largest single batch of infrared parallaxes for brown dwarfs to date. Our parallaxes have a median uncertainty of 3.5mas, similar to most previous ground-based infrared parallax surveys. Our target list was designed to complete a volume-limited parallax sample of L0-T8 dwarfs out to 25pc spanning declinations -30{deg} to +60{deg} (68% of the sky). We report the first parallaxes for 165 objects, and we improve on previous measurements for another 53 objects. Our targets include 104 objects (mostly early-L dwarfs) having Gaia DR2 parallax measurements with which our parallaxes are consistent. We include an extensive comparison of previous literature parallaxes for L and T dwarfs with both our results and Gaia DR2 measurements, identifying systematic offsets for some previous surveys. Our parallaxes confirm that 14 objects previously identified as wide common proper motion companions to main-sequence stars have distances consistent with companionship. We also report new J_MKO_ photometry for our targets, including the first measurements for 193 of our targets and improvements over previously published J_MKO_ photometry for another 60 targets. Altogether, our parallaxes will enable the first population studies using a volume-limited sample spanning spectral types L0-T8 defined entirely by parallaxes.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/127/3137
- Title:
- Hawaii redshifts in the ACS-GOODS region
- Short Name:
- J/AJ/127/3137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of an extensive spectroscopic survey of galaxies in the roughly 160 arcmin^2^ ACS-GOODS region surrounding the Hubble Deep Field North (HDF-N). We have identified 892 galaxies or stars with z<24, R<24.5, or B<25 in the region. The spectra were obtained with either the DEIMOS or LRIS spectrographs on the Keck 10m telescopes. The results are compared with photometric redshift estimates and with redshifts from the literature, as well as with the redshifts of a parallel effort led by a group at Keck. Our sample, when combined with the literature data, provides identifications for 1324 sources. We use our results to determine the redshift distributions with magnitude, to analyze the rest-frame color distributions with redshift and spectral type, and to investigate the dependence of the X-ray galaxy properties on the local galaxy density in the redshift interval z=0-1.5. We find the rather surprising result that the galaxy X-ray properties are not strongly dependent on the local galaxy density for galaxies in the same luminosity range.
- ID:
- ivo://CDS.VizieR/J/MNRAS/461/1734
- Title:
- HAWK-I JHK photometry of the Orion Nebula Cloud
- Short Name:
- J/MNRAS/461/1734
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Due to its youth, proximity and richness, the Orion nebula cloud (ONC) is an ideal testbed to obtain a comprehensive view on the initial mass function (IMF) down to the planetary mass regime. Using the HAWK-I camera at the VLT, we have obtained an unprecedented deep and wide near-infrared JHK mosaic of the ONC (90 per cent completeness at K ~19.0mag, 22x28 arcmin^2^). Applying the most recent isochrones and accounting for the contamination of background stars and galaxies, we find that ONC's IMF is bimodal with distinct peaks at about 0.25 and 0.025M_{sun}_ separated by a pronounced dip at the hydrogen burning limit (0.08M_{sun}_), with a depth of about a factor of 2-3 below the log-normal distribution. Apart from ~920 low-mass stars (M<1.4M_{sun}_) the IMF contains ~760 brown dwarf candidates and ~160 isolated planetary mass object candidates with M>0.005M_{sun}_, hence about 10 times more substellar candidates than known before. The substellar IMF peak at 0.025M_{sun}_ could be caused by brown dwarfs and isolated planetary mass objects which have been ejected from multiple systems during the early star formation process or from circumstellar discs.
- ID:
- ivo://CDS.VizieR/J/AJ/155/122
- Title:
- HAZMAT. III. Low-mass stars GALEX photometry
- Short Name:
- J/AJ/155/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-mass stars are currently the most promising targets for detecting and characterizing habitable planets in the solar neighborhood. However, the ultraviolet (UV) radiation emitted by such stars can erode and modify planetary atmospheres over time, drastically affecting their habitability. Thus, knowledge of the UV evolution of low-mass stars is critical for interpreting the evolutionary history of any orbiting planets. Shkolnik & Barman (2014, J/AJ/148/64) used photometry from the Galaxy Evolution Explorer (GALEX) to show how UV emission evolves for early-type M stars (>0.35 M_{sun}_). In this paper, we extend their work to include both a larger sample of low-mass stars with known ages as well as M stars with lower masses. We find clear evidence that mid- and late-type M stars (0.08-0.35 M_{sun}_) do not follow the same UV evolutionary trend as early-Ms. Lower-mass M stars retain high levels of UV activity up to field ages, with only a factor of 4 decrease on average in GALEX NUV and FUV flux density between young (<50 Myr) and old (~5 Gyr) stars, compared to a factor of 11 and 31 for early-Ms in NUV and FUV, respectively. We also find that the FUV/NUV flux density ratio, which can affect the photochemistry of important planetary biosignatures, is mass- and age-dependent for early-Ms, but remains relatively constant for the mid- and late-type Ms in our sample.
- ID:
- ivo://CDS.VizieR/J/AJ/154/67
- Title:
- HAZMAT. II. Low-mass stars with GALEX UV observations
- Short Name:
- J/AJ/154/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ultraviolet (UV) light from a host star influences a planet's atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope. These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer (GALEX) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771-2831{AA}) and far-ultraviolet (FUV; 1344-1786{AA}). Within 30pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.
- ID:
- ivo://CDS.VizieR/J/ApJ/872/17
- Title:
- HAZMAT. V. UV and X-ray evolution of K stars
- Short Name:
- J/ApJ/872/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowing the high-energy radiation environment of a star over a planet's formation and evolutionary period is critical in determining if that planet is potentially habitable and if any biosignatures could be detected, as UV radiation can severely change or destroy a planet's atmosphere. Current efforts for finding a potentially habitable planet are focused on M stars, yet K stars may offer more habitable conditions due to decreased stellar activity and more distant and wider habitable zones (HZs). While M star activity evolution has been observed photometrically and spectroscopically, there has been no dedicated investigation of K star UV evolution. We present the first comprehensive study of the near-UV, far-UV, and X-ray evolution of K stars. We used members of young moving groups and clusters ranging in age from 10 to 625Myr combined with field stars and their archived GALEX UV and ROSAT X-ray data to determine how the UV and X-ray radiation evolve. We find that the UV and X-ray flux incident on an HZ planet is 5-50 times lower than that of HZ planets around early-M stars and 50-1000 times lower than those around late-M stars, due to both an intrinsic decrease in K dwarf stellar activity occurring earlier than for M dwarfs and the more distant location of the K dwarf HZ.
- ID:
- ivo://CDS.VizieR/J/A+A/403/493
- Title:
- H-band observation of Chandra Deep Field South
- Short Name:
- J/A+A/403/493
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report preliminary results of our H-band survey of the Chandra Deep Field South (CDFS). The observations were made using SofI on the NTT, and cover 0.027 square degrees with a 50% completeness limit of H=20.5, and 0.17 square degrees with a 50% completeness limit of H=19.8. We used SExtractor to extract sources from our fields. In total we have detected 4819 objects. Star-galaxy separation was performed using the SExtractor parameter "stellarity index". All objects with an index of 0.5 or lower were classified as galaxies. According to this criterion, 80% of our detections are galaxies. We then compare our results with previous observations of the CDFS. Our astrometric solutions are in good agreement with the Las Campanas Infrared Survey (LCIRS), the COMBO-17 and the ESO-EIS surveys. The photometry of our catalog compares satisfactorily with the results of the LCIRS, as well as with the GOODS data. Galaxy number counts are presented and compared with the LCIRS results. The present data are intended to complement the recent and future multi-wavelength observations of the CDFS and will be used, in conjunction with additional multiband photometry, to find counterparts of the upcoming mid-infrared surveys with SIRTF.
- ID:
- ivo://CDS.VizieR/J/A+A/414/905
- Title:
- H-band photometry in Pisces-Perseus disk galaxies
- Short Name:
- J/A+A/414/905
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the scaling relations of bulge and disk structural parameters for a sample of 108 disk galaxies. Structural parameters of individual galaxies are obtained from two-dimensional bulge/disk decomposition of their H-band surface brightness distributions. Bulges are modelled with a generalized exponential (Sersic) with variable integer shape index n.
- ID:
- ivo://CDS.VizieR/J/A+AS/137/101
- Title:
- H-band photometry in Pisces-Perseus spirals
- Short Name:
- J/A+AS/137/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper presents results of an H-band imaging survey of spiral galaxies in the Perseus-Pisces supercluster area. The derived global photometric parameters of the sample galaxies (magnitudes, diameters, etc.) are collected in Table 3.
- ID:
- ivo://CDS.VizieR/J/A+A/513/L3
- Title:
- H-band thermal emission of exoplanet WASP-19b
- Short Name:
- J/A+A/513/L3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first ground-based detection of thermal emission from an exoplanet in the H-band. Using HAWK-I on the VLT, we observed an occultation of WASP-19b by its G8V-type host star. WASP-19b is a Jupiter-mass planet with an orbital period of only 19 h, and thus, being highly irradiated, is expected to be hot. We measure an H-band occultation depth of (0.259^+0.046^_-0.044_)%, which corresponds to an H-band brightness temperature of T_H_=2580+/-125K. A cloud-free model of the planet's atmosphere, with no redistribution of energy from day-side to night-side, under predicts the planet/star flux density ratio by a factor of two. As the stellar parameters, and thus the level of planetary irradiation, are well-constrained by measurement, it is likely that our model of the planet's atmosphere is too simple.
