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Title:
Trigonometric parallaxes of ten ultracool subdwarfs
Authors:
Schilbach, E.; Röser, S.; Scholz, R.-D.
Affiliation:
AA(Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany ), AB(Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany ), AC(Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany )
Publication:
Astronomy and Astrophysics, Volume 493, Issue 2, 2009, pp.L27-L30 (A&A Homepage)
Publication Date:
01/2009
Origin:
EDP Sciences
Astronomy Keywords:
astrometry, stars: distances, stars: kinematics, stars: low-mass, brown dwarfs, subdwarfs, solar neighborhood
DOI:
10.1051/0004-6361:200811281
Bibliographic Code:
2009A&A...493L..27S

Abstract

Aims: We measure absolute trigonometric parallaxes and proper motions with respect to many background galaxies for a sample of ten ultracool subdwarfs.
Methods: Observations were taken in the H-band with the OMEGA2000 camera on the 3.5 m-telescope at Calar Alto, Spain during a time period of 3.5 years. For the first time, the reduction of the astrometric measurements was carried out directly with respect to background galaxies. We obtained absolute parallaxes with mean errors ranging between 1 and 3 mas.
Results: With six completely new parallaxes we more than doubled the number of benchmark ultracool (>sdM7) subdwarfs. Six stars in the MK_s vs. J-Ks diagram fit perfectly to model subdwarf sequences from M7 to L4 with [M/H] between -1.0 and -1.5, whereas 4 are consistent with a moderately low metallicity ([M/H]=-0.5) from M7 to T6. All but one of our objects have large tangential velocities between 200 and 320 km s-1 typical of the Galactic halo population. Our results are in good agreement with recent independent measurements for three of our targets and confirm the previously measured parallax and absolute magnitude MK_s of the nearest and coolest (T-type) subdwarf 2MASS 0937+29 with higher accuracy. For all targets, we also obtained infrared J,H,Ks photometry at a level of a few milli-magnitudes relative to 2MASS standards.

Based on observations collected with Omega 2000 at the 3.5 m telescope at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Tables 1 and 2 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/493/L27

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