HVS 7

HVS 7 -- hyper-velocity star 7, otherwise known as SDSS J113312.12+010824.9 is a rare star that has been accelerated to faster than our Milky Way Galaxy's escape velocity.^[7][8] In 2013 a team under N. Przybilla wrote that the star had a chemically peculiar photosphere, which masked its origins.^[7] The star was first cataloged during the Sloan Digital Sky Survey. It was identified as a hyper-velocity star in 2006.^[8]

HVS 7

Observation data Epoch J2000      Equinox J2000
Constellation	Leo
Right ascension	11h 33m 12.125s[1]
Declination	+01° 08′ 24.87″[1]
Apparent magnitude (V)	17.80[2]
Characteristics
Spectral type	sdB[3]
Astrometry
Radial velocity (Rv)	518[4] km/s
Proper motion (μ)	RA: -1[5] mas/yr Dec.: 1[5] mas/yr
Distance	180,000 ly (55,000[6] pc)
Details[7]
Mass	3.7 M☉
Radius	4.0 R☉
Luminosity	300 L☉
Surface gravity (log g)	3.8 cgs
Temperature	12,000 K
Rotational velocity (v sin i)	55 km/s
Age	150 Myr
Other designations
SDSS J113312.12+010824.9, EPIC 201540171
Database references
SIMBAD	data

The star has a chemically peculiar spectrum, roughly matching a B-type subdwarf. Stars in this region of the Hertzsprung–Russell diagram are expected to either be hot horizontal branch stars, low-mass helium-burning objects, or moderate mass hydrogen-burning stars slightly below the main sequence. The high rotational velocity of HVS 7 means it is likely to be a young star near the main sequence, around 150 million years old and 3.7 times the mass of the sun.^[7]

References

1. Adelman-McCarthy, Jennifer K. (2008). "The Sixth Data Release of the Sloan Digital Sky Survey". The Astrophysical Journal Supplement Series. 175 (2): 297–313. arXiv:0707.3413. Bibcode:2008ApJS..175..297A. doi:10.1086/524984. S2CID 7699771.
2. Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.; Bromley, Benjamin C. (2007). "Hypervelocity Stars. III. The Space Density and Ejection History of Main-Sequence Stars from the Galactic Center". The Astrophysical Journal. 671 (2): 1708. arXiv:0709.1471. Bibcode:2007ApJ...671.1708B. doi:10.1086/523642. S2CID 15074398.
3. Harris, Hugh C.; Liebert, James; Kleinman, S. J.; Nitta, Atsuko; Anderson, Scott F.; Knapp, Gillian R.; Krzesiński, Jurek; Schmidt, Gary; Strauss, Michael A.; Vanden Berk, Dan; Eisenstein, Daniel; Hawley, Suzanne; Margon, Bruce; Munn, Jeffrey A.; Silvestri, Nicole M.; Smith, J. Allyn; Szkody, Paula; Collinge, Matthew J.; Dahn, Conard C.; Fan, Xiaohui; Hall, Patrick B.; Schneider, Donald P.; Brinkmann, J.; Burles, Scott; Gunn, James E.; Hennessy, Gregory S.; Hindsley, Robert; Ivezić, Zeljko; Kent, Stephen; et al. (2003). "An Initial Survey of White Dwarfs in the Sloan Digital Sky Survey". The Astronomical Journal. 126 (2): 1023. arXiv:astro-ph/0305347. Bibcode:2003AJ....126.1023H. doi:10.1086/376842. S2CID 118927660.
4. Adelman-Mccarthy, J. K.; et al. (2011). "VizieR Online Data Catalog: The SDSS Photometric Catalog, Release 8 (Adelman-McCarthy+, 2011)". VizieR On-line Data Catalog. Bibcode:2011yCat.2306....0A.
5. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
6. Brown, Warren R. (2006). "Hypervelocity Stars. I. The Spectroscopic Survey". The Astrophysical Journal. 647 (1): 303–311. arXiv:astro-ph/0604111. Bibcode:2006ApJ...647..303B. doi:10.1086/505165. S2CID 15561164.
7. Przybilla, N.; Nieva, M. F.; Tillich, A.; Heber, U.; Butler, K.; Brown, W. R. (2008). "HVS 7: A chemically peculiar hyper-velocity star". Astronomy & Astrophysics. 488 (2): L51–L54. arXiv:0810.0864. Bibcode:2008A&A...488L..51P. doi:10.1051/0004-6361:200810455. S2CID 56111543. Such a surface abundance pattern is caused by atomic diffusion in a possibly magnetically stabilised, non-convective atmosphere. Hence all chemical information on the star's place of birth and its evolution has been washed out. High precision astrometry is the only means to validate a GC origin for HVS 7.
8. Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J. (2006). "Hypervelocity Stars. I. The Spectroscopic Survey". The Astrophysical Journal. 647 (1): 303–311. arXiv:astro-ph/0604111. Bibcode:2006ApJ...647..303B. doi:10.1086/505165. S2CID 15561164. Here we report the two most recently discovered HVSs: SDSS J110557.45+093439.5 and possibly SDSS J113312.12+010824, traveling with Galactic rest-frame velocities at least +508+/-12 and +418+/-10 km s-1, respectively.