J/ApJ/751/55 MMT hypervelocity star survey. II. (Brown+, 2012)
MMT hypervelocity star survey.
II. Five new unbound stars.
Brown W.R., Geller M.J., Kenyon S.J.
<Astrophys. J., 751, 55 (2012)>
=2012ApJ...751...55B 2012ApJ...751...55B
ADC_Keywords: Surveys ; Milky Way ; Stars, halo ; Radial velocities ;
Photometry, SDSS ; Stars, B-type
Keywords: galaxies: individual (M31, Sextans B) - Galaxy: center -
Galaxy: halo - Galaxy: kinematics and dynamics - stars: early-type
Abstract:
We present the discovery of five new unbound hypervelocity stars
(HVSs) in the outer Milky Way halo. Using a conservative estimate of
Galactic escape velocity, our targeted spectroscopic survey has now
identified 16 unbound HVSs as well as a comparable number of HVSs
ejected on bound trajectories. A Galactic center origin for the HVSs
is supported by their unbound velocities, the observed number of
unbound stars, their stellar nature, their ejection time distribution,
and their Galactic latitude and longitude distribution. Other proposed
origins for the unbound HVSs, such as runaway ejections from the disk
or dwarf galaxy tidal debris, cannot be reconciled with the
observations. An intriguing result is the spatial anisotropy of HVSs
on the sky, which possibly reflects an anisotropic potential in the
central 10-100pc region of the Galaxy. Further progress requires
measurement of the spatial distribution of HVSs over the southern sky.
Our survey also identifies seven B supergiants associated with known
star-forming galaxies; the absence of B supergiants elsewhere in the
survey implies there are no new star-forming galaxies in our survey
footprint to a depth of 1-2Mpc.
Description:
Our HVS Survey is a concatenation of candidates selected from SDSS
DR6, DR7, and DR8 (see section 2.1).
We obtained spectroscopy for 497 candidates at the 6.5m MMT telescope
during observing runs spanning 2008 December to 2011 October, with
a wavelength coverage 3600-4500Å and a spectral resolution of
1-1.2Å. The average statistical uncertainty of the radial velocity
measurements is ±11km/s.
While we made an effort not to observe stars with existing
spectroscopy, SDSS re-observed 245 of our stars as part of SEGUE
(Yanny et al. 2009, Cat. J/AJ/137/4377).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 78 39 HVS survey stars with vrf>+275km/s
table2.dat 71 955 *Late B-type halo stars in the HVS survey
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Note on table2.dat: For completeness, we provide both the 375 newly
observed objects and the 580 previously reported objects.
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
J/AJ/139/59 : Milky Way halo velocity dispersion profile (Brown+, 2010)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/ApJ/671/1708 : Hypervelocity stars. III (Brown+, 2007)
J/ApJ/660/311 : Hypervelocity stars. II. (Brown+, 2007)
J/ApJ/647/303 : Spectroscopic survey of hypervelocity stars (Brown+, 2006)
J/AJ/126/1362 : Century Survey Galactic Halo Project. I. (Brown+, 2003)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Type Type of hypervelocity star (1)
8- 10 A3 --- --- [HVS ]
11- 12 I2 --- HVS [1/21]? High Velocity Star number if any,
<[BGK2006] HV NN> in Simbad
14- 16 I3 km/s HRV Heliocentric radial velocity
18- 20 I3 km/s Vrf Minimum Galactic rest-frame velocity vrf
(not a full space velocity) (G1)
22- 26 F5.2 mag gmag0 De-reddened SDSS g-band magnitude (2)
28- 32 F5.2 mag gMag Absolute magnitude
34- 36 I3 kpc Dist Galactocentric distance R
38- 43 F6.2 deg GLON Galactic longitude
45- 50 F6.2 deg GLAT Galactic latitude
52- 76 A25 --- Name Main identifier
78 I1 --- Ref ? Reference (3)
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Note (1): Type as follows:
HVSs = unbound hypervelocity stars (18) stars
pHVSs = possible hypervelocity stars (5 stars)
pBHVSs = possibly bound hypervelocity stars (16 stars)
Note (2): Absolute magnitude Mg from Girardi et al. (2002A&A...391..195G 2002A&A...391..195G,
2004A&A...422..205G 2004A&A...422..205G) main-sequence tracks
Note (3): References as follows:
1 = Brown et al. 2005ApJ...622L..33B 2005ApJ...622L..33B;
2 = Hirsch et al. 2005A&A...444L..61H 2005A&A...444L..61H;
3 = Edelmann et al. 2005ApJ...634L.181E 2005ApJ...634L.181E;
4 = Brown et al. 2006ApJ...640L..35B 2006ApJ...640L..35B;
5 = Brown et al. 2006, Cat. J/ApJ/647/303 (<[BGK2006] HV NN> in Simbad)
6 = Brown et al. 2007, Cat. J/ApJ/671/1708 (<[BGK2006] HV NN> in Simbad)
7 = Brown et al. 2009ApJ...690.1639B 2009ApJ...690.1639B
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Hour of Right Ascension (J2000)
4- 5 I2 min RAm Minute of Right Ascension (J2000)
7- 12 F6.3 s RAs Second of Right Ascension (J2000)
14 A1 --- DE- Sign of the Declination (J2000)
15- 16 I2 deg DEd Degree of Declination (J2000)
18- 19 I2 arcmin DEm Arcminute of Declination (J2000)
21- 25 F5.2 arcsec DEs Arcsecond of Declination (J2000)
27- 32 F6.3 mag gmag SDSS g band apparent magnitude
34- 38 F5.3 mag e_gmag Uncertainty in gmag
40- 45 F6.1 km/s HRV Heliocentric radial velocity from this study
47- 50 F4.1 km/s e_HRV Uncertainty in HRV
52- 57 F6.1 km/s Vrf Velocity in Galactic rest frame (G1)
59- 64 F6.2 deg GLON Galactic longitude
66- 71 F6.2 deg GLAT Galactic latitude
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Global Notes:
Note (G1): velocity defined by Eq.1, assuming a 250km/s circular rotation
velocity: vrf = HRV + 11.1cos(l)cos(b) + 262.24sin(l)cos(b) + 7.25sin(b).
History:
From electronic version of the journal
References:
Brown et al. Paper I. 2009ApJ...690.1639B 2009ApJ...690.1639B
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 21-Jun-2013