AN EXTREMELY FAST HALO HOT SUBDWARF STAR IN A WIDE BINARY SYSTEM

Nemeth P, Ziegerer E, Irrgang A, Geier S, Fuerst F, Kupfer T, Heber U (2016)

Publication Status: Published

Publication Type: Journal article

Publication year: 2016

Journal

Publisher: IOP PUBLISHING LTD

Book Volume: 821

Article Number: ARTN L13

Journal Issue: 1

DOI: 10.3847/2041-8205/821/1/L13

Abstract

New spectroscopic observations of the halo hyper-velocity star candidate SDSS J121150.27+143716.2 (V = 17.92 mag) revealed a cool companion to the hot subdwarf primary. The components have a very similar radial velocity and their absolute luminosities are consistent with the same distance, confirming the physical nature of the binary, which is the first double-lined hyper-velocity candidate. Our spectral decomposition of the Keck/ESI spectrum provided an sdB+K3V pair, analogous to many long-period subdwarf binaries observed in the Galactic disk. We found the subdwarf atmospheric parameters: T-eff = 30 600 +/- 500 K, log g= 5.57 +/- 0.06 cm s(-2), and He abundance log(nHe/nH)= -3.0 +/- 0.2. Oxygen is the most abundant metal in the hot subdwarf atmosphere, and Mg and Na lines are the most prominent spectral features of the cool companion, consistent with a metallicity of [Fe/H] = -1.3. The non-detection of radial velocity variations suggest the orbital period to be a few hundred days, in agreement with similar binaries observed in the disk. Using the SDSS-III flux calibrated spectrum we measured the distance to the system d = 5.5 +/- 0.5 kpc, which is consistent with ultraviolet, optical, and infrared photometric constraints derived from binary spectral energy distributions. Our kinematic study shows that the Galactic rest-frame velocity of the system is so high that an unbound orbit cannot be ruled out. On the other hand, a bound orbit requires a massive dark matter halo. We conclude that the binary either formed in the halo or was accreted from the tidal debris of a dwarf galaxy by the Milky Way.

Authors with CRIS profile

Involved external institutions

California Institute of Technology (Caltech) United States (USA) (US)

How to cite

APA:

Nemeth, P., Ziegerer, E., Irrgang, A., Geier, S., Fuerst, F., Kupfer, T., & Heber, U. (2016). AN EXTREMELY FAST HALO HOT SUBDWARF STAR IN A WIDE BINARY SYSTEM. Astrophysical Journal Letters, 821(1). https://doi.org/10.3847/2041-8205/821/1/L13

MLA:

Nemeth, Peter, et al. "AN EXTREMELY FAST HALO HOT SUBDWARF STAR IN A WIDE BINARY SYSTEM." Astrophysical Journal Letters 821.1 (2016).

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