arXiv subjects

Harry H. Guetter

Publications and source records attributed to Harry H. Guetter.

6 recordsLinked to original sources

arXiv2026

Parallaxes, Proper Motions, and Near-Infrared Photometry for 173 L and T Dwarfs From The US Naval Observatory Infrared Astrometry Program

We present near-infrared parallax and proper motion astrometry for 74 L-dwarfs and 99 T-dwarfs, as single objects or in binary systems, obtained with the ASTROCAM astrometric imager on the USNO, Flagstaff Station 1.55-m telescope over two observing periods. For all 173 objects the median number of observational epochs was 62 with a median time frame of 5.25 years, resulting in median uncertainties of $σ$($π_{abs}$) = 1.51 mas, $σ$($μ_{abs}$) = 1.02 mas yr$^{-1}$, and $σ$($V_{\rm tan}$) = 1.01 km s$^{-1}$. Our observations provide the first parallax/proper motion results for 16 objects and the highest precision parallaxes/proper motions for an additional 116 objects. A serendipitous overlap of 40 objects with Gaia DR3 astrometry allows direct comparison and confirmation of our results, along with an investigation on the effects of resolved binarity on astrometric results. We also provide a uniform set of $J$-, $H$-, $K_{S}$-band photometry in the UKIRT/MKO system, most of it being from new observations. We use these results to examine objects included in this study of special-interest populations, consisting of binaries, wide companions, young objects, subdwarfs, and brown dwarf spectral standards.

astro-ph.SR↗

arXiv2018

Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample

This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station (NOFS) between 1989 and 2017, and the average uncertainty in the parallax values is 0.6 mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric dataset which spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for nineteen stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a sub-sample of 179 white dwarfs (WDs) at distances of 25 - 200 pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass and cooling age of each WD. Twenty-six WDs are newly classified and twelve systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of < 8 Gyr and masses close to the canonical 0.6 M_Sun.

astro-ph.SR↗

arXiv2017

CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station (NOFS) are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here is new or updated $VI$ photometry on the Johnson-Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS $JHK_s$ near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Since large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.

astro-ph.SR↗

arXiv2007

Parallax and Luminosity Measurements of an L Subdwarf

We present the first parallax and luminosity measurements for an L subdwarf, the sdL7 2MASS J05325346+8246465. Observations conducted over three years by the USNO infrared astrometry program yield an astrometric distance of 26.7+/-1.2 pc and a proper motion of 2.6241+/-0.0018"/yr. Combined with broadband spectral and photometric measurements, we determine a luminosity of log(Lbol/Lsun) = -4.24+/-0.06 and Teff = 1730+/-90 K (the latter assuming an age of 5-10 Gyr), comparable to mid-type L field dwarfs. Comparison of the luminosity of 2MASS J05325346+8246465 to theoretical evolutionary models indicates that its mass is just below the sustained hydrogen burning limit, and is therefore a brown dwarf. Its kinematics indicate a ~110 Myr, retrograde Galactic orbit which is both eccentric (3 <~ R <~ 8.5 kpc) and extends well away from the plane (Delta_Z = +/-2 kpc), consistent with membership in the inner halo population. The relatively bright J-band magnitude of 2MASS J05325346+8246465 implies significantly reduced opacity in the 1.2 micron region, consistent with inhibited condensate formation as previously proposed. Its as yet unknown subsolar metallicity remains the primary limitation in constraining its mass; determination of both parameters would provide a powerful test of interior and evolutionary models for low-mass stars and brown dwarfs.

astro-ph↗

arXiv2006

Trigonometric Parallaxes of Central Stars of Planetary Nebulae

Trigonometric parallaxes of 16 nearby planetary nebulae are presented, including reduced errors for seven objects with previous initial results and results for six new objects. The median error in the parallax is 0.42 mas, and twelve nebulae have parallax errors less than 20 percent. The parallax for PHL932 is found here to be smaller than was measured by Hipparcos, and this peculiar object is discussed. Comparisons are made with other distance estimates. The distances determined from these parallaxes tend to be intermediate between some short distance estimates and other long estimates; they are somewhat smaller than estimated from spectra of the central stars. Proper motions and tangential velocities are presented. No astrometric perturbations from unresolved close companions are detected.

astro-ph↗

arXiv2000

The Discovery of an Embedded Cluster of High-Mass Stars Near SGR 1900+14

Deep I-band imaging to approximately I = 26.5 of the soft gamma-ray repeater SGR 1900+14 region has revealed a compact cluster of massive stars located only a few arcseconds from the fading radio source thought to be the location of the SGR (Frail, Kulkarni, & Bloom 1999). This cluster was previously hidden in the glare of the pair of M5 supergiant stars (whose light was removed by PSF subtraction) proposed by Vrba et al. (1996) as likely associated with the SGR 1900+14. The cluster has at least 13 members within a cluster radius of approximately 0.6 pc, based on an estimated distance of 12-15 kpc. It is remarkably similar to a cluster found associated with SGR 1806-20 (Fuchs et al. 1999). That similar clusters have now been found at or near the positions of the two best-studied SGRs suggests that young neutron stars, thought to be responsible for the SGR phenomenon, have their origins in proximate compact clusters of massive stars.

astro-ph↗