An ancient F-type subdwarf from the halo crossing the Galactic plane
Abstract
Aims: We selected the bluest object, WISE J0725-2351, from Luhman's new high proper motion (HPM) survey based on observations with the Wide-field Infrared Survey Explorer (WISE) for spectroscopic follow-up observations. Our aim was to unravel the nature of this relatively bright (V ~ 12, J ~ 11) HPM star (μ = 267 mas/yr).
Methods: We obtained low- and medium-resolution spectra with the European Southern Observatory (ESO) New Technology Telescope (NTT)/EFOSC2 and Very Large Telescope (VLT)/X-Shooter instruments, investigated the radial velocity and performed a quantitative spectral analysis that allowed us to determine physical parameters. The fit of the spectral energy distribution based on the available photometry to low-metallicity model spectra and the similarity of our target to a metal-poor benchmark star (HD 84937) allowed us to estimate the distance and space velocity.
Results: As in the case of HD 84937, we classified WISE J0725-2351 as sdF5: or a metal-poor turnoff star with [ Fe/H ] = -2.0 ± 0.2, Teff = 6250 ± 100 K, log g = 4.0 ± 0.2, and a possible age of about 12 Gyr. At an estimated distance of more than 400 pc, its proper motion translates to a tangential velocity of more than 500 km s-1. Together with its constant (on timescales of hours, days, and months) and large radial velocity (about +240 km s-1), the resulting Galactic restframe velocity is about 460 km s-1, implying a bound retrograde orbit for this extreme halo object that currently crosses the Galactic plane at high speed.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 2015
- DOI:
- 10.1051/0004-6361/201425471
- arXiv:
- arXiv:1501.00929
- Bibcode:
- 2015A&A...574A..96S
- Keywords:
-
- proper motions;
- stars: distances;
- stars: kinematics and dynamics;
- stars: Population II;
- subdwarfs;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 8 pages, 3 tables, 7 figures, accepted for publication in Astronomy and Astrophysics