2011A&A...527A.137T


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.13CEST07:04:44

2011A&A...527A.137T - Astronomy and Astrophysics, volume 527A, 137-137 (2011/3-1)

The Hyper-MUCHFUSS project: probing the Galactic halo with sdB stars.

TILLICH A., HEBER U., GEIER S., HIRSCH H., MAXTED P.F.L., GAENSICKE B.T., MARSH T.R., NAPIWOTZKI R., OSTENSEN R.H. and SCHOLZ R.-D.

Abstract (from CDS):

High-velocity stars in the Galactic halo, e.g. the so-called hyper-velocity stars (HVS), are important tracers of the properties of the dark matter halo, in particular its mass. A search for the fastest stars among hot subdwarfs (sdB) in the halo is carried out to identify HVS, unbound to the Galaxy, and bound population II stars, in order to derive a lower limit to the halo mass. Based on the SDSS DR6 spectral database we selected stars with high rest-frame velocities. These radial velocity (RV) measurements were verified at several telescopes to exclude RV variable stars. Out of 88 stars observed in the follow-up campaign, 39 stars were found to have constant RVs. For twelve of them we measured a proper motion significantly different from zero and obtained spectroscopic distances from quantitative spectral analysis to construct the full 6D phase space information for a kinematical study. All but one programme sdB show halo characteristics, but can be distinguished as two kinematical groups, one (G1) with the low Galactic rotation typical of halo stars and a second one (G2) with rapid retrograde motion. We also investigate the possibility that the programme stars are not genuine halo stars but ejected from the Galactic disc or bulge. The G1 objects crossed the Galactic plane in the central bulge, whereas the G2 stars did so in the outer Galactic disc. J1211+1437 (G2) is an HVS candidate, as it is unbound to the Galaxy if the standard Galactic potential is adopted. We conclude that in the ejection scenario, G1 stars might have been formed via the slingshot mechanism that invokes acceleration by tidal interaction of a binary with the central supermassive black hole. The G2 stars, however, would originate in the outskirts of the Galactic disc and not in the central bulge. J1211+1437 is the first unbound subdwarf B star, for which we can rule out the slingshot mechanism. Alternatively, we may assume that the stars are old population II stars and so they have to be bound. Then the kinematics of J1211+1437 set a lower limit of 2x1012M to the mass of the Galactic dark matter halo.

Abstract Copyright:

Journal keyword(s): stars: kinematics and dynamics - subdwarfs - line: profiles - proper motions - Galaxy: halo - stars: atmospheres

Simbad objects: 18

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Number of rows : 18

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 M 32 IG 00 42 41.825 +40 51 54.61 9.51 9.03 8.08     ~ 2010 2
2 SDSS J084447.00+113910.0 HS* 08 44 47.0060179863 +11 39 10.111962790           sdB 4 0
3 SDSS J084556.85+135211.3 HS* 08 45 56.8467213067 +13 52 11.311275688           sdB 4 0
4 WD 0846+151 WD* 08 49 38.8638791733 +14 55 03.187550466   19.0   18.9   DA 6 0
5 US 708 HS* 09 33 20.8630614743 +44 17 05.503100302   18.5 18.8     sdOHe 71 0
6 SDSS J094850.47+551631.7 WD* 09 48 50.4739199345 +55 16 31.743422836   18.6   19.3   DAB 6 0
7 SDSS J102057.16+013751.2 HS* 10 20 57.1588866800 +01 37 51.318942165   16.6   16.6 17.00 sdB 8 0
8 PB 3877 WD* 12 11 50.2653712012 +14 37 16.205983104   17.5       DAB 17 0
9 [SS59] II 135 HV* 12 22 29.6071406987 +40 49 35.561457102   11.53 11.85     B4V 45 0
10 SDSS J135824.61+472931.6 WD* 13 58 24.5861848419 +47 29 31.498202748           DA 7 0
11 SDSS J155635.80+470851.8 HS* 15 56 35.8019099523 +47 08 51.775040619           sdB 3 0
12 SDSS J163213.05+205124.0 WD* 16 32 13.0552512171 +20 51 24.091558962   17.5   17.6   DAB 6 0
13 SDSS J164419.45+452326.7 HS* 16 44 19.4487065349 +45 23 26.787286274   17.0   17.4   sdB 11 0
14 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 11542 0
15 PB 5010 HS* 21 56 48.7158870914 +00 36 20.790611748   17.8   18.2   sdO 9 0
16 PB 5146 HS* 22 44 51.8181616615 +01 06 31.011879879   18.4   18.2   sdBp 9 0
17 HD 217791 * 23 03 22.4699478320 -20 06 33.513682023   10.31 9.22     K1III 4 0
18 NAME Galactic Bulge reg ~ ~           ~ 3391 0

    Equat.    Gal    SGal    Ecl

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2020.07.13-07:04:44

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