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V391 Pegasi - Wikipedia

Coordinates:

22^h 04^m 12.2^s, +26° 25′ 08″

From Wikipedia, the free encyclopedia

V391 Pegasi
Observation data Epoch J2000.0 Equinox J2000.0
A light curve for V391 Pegasi, adapted from Silvotti et al. (2010)^[1]
Constellation	Pegasus
Right ascension	22^h 04^m 12.1045^s^[2]
Declination	+26° 25′ 07.819″^[2]
Apparent magnitude (V)	+14.61^[3]
Characteristics
Evolutionary stage	subdwarf B
Spectral type	sdB^[4]
Variable type	V361 Hydrae (sdBV_r)^[5]
Astrometry

Proper motion (μ)	RA: −4.906(40) mas/yr^[2] Dec.: −3.703(34) mas/yr^[2]
Parallax (π)	0.7388 ± 0.0327 mas^[2]
Distance	4,400 ± 200 ly (1,350 ± 60 pc)
Absolute magnitude (M_V)	+3.88^[4]

Details

Mass	0.47^[4] `M`_☉
Radius	0.23^[4] `R`_☉
Luminosity	34^[4] `L`_☉
Surface gravity (log g)	5.4±0.1^[6] cgs
Temperature	29,300±500^[6] K
Age	>10^[7] Gyr

Other designations
HS 2201+2610, 2MASS J22041211+2625078
Database references
SIMBAD	data

V391 Pegasi, also catalogued as HS 2201+2610, is a blue-white subdwarf star approximately 4,400 light-years away in the constellation of Pegasus. The star is classified as an "extreme horizontal branch star". It is small, with only half the mass and a bit less than one quarter the diameter of the Sun. It has luminosity 34 times that of the Sun. It could be quite old, perhaps in excess of 10 Gyr. It is a pulsating variable star of the V361 Hydrae type (or also called sdBV_r type). It is believed that the star's mass when it was still on the main sequence was between 0.8 and 0.9 times that of the Sun.^[7]

Formation

Subdwarf B stars such as V391 Pegasi are thought to be the result of the ejection of the hydrogen envelope of a red giant star at or just before the onset of helium fusion. The ejection left only a tiny amount of hydrogen on the surface—less than 1/1000 of the total stellar mass. The future for the star is to eventually cool down to make a low-mass white dwarf. Most stars retain more of their hydrogen after the first red giant phase, and eventually become asymptotic giant branch stars. The reason that some stars, like V391 Pegasi, lose so much mass is not well known.^[4] At the tip of the red-giant branch, the red giant precursors of the subdwarf stars reach their maximum radius, on the order of 0.7 AU.^[7] After this point, the hydrogen envelope is lost and helium fusion begins—this is known as the helium flash.

Hypothesized planetary system

In 2007, research using the variable star timing method indicated the presence of a gas giant planet orbiting V391 Pegasi.^[7] This planet was designated V391 Pegasi b. This planet around an "extreme horizontal branch" star provided clues about what could happen to the planets in the Solar System when the Sun turns into a red giant within the next 5 billion years.^[8]

However, subsequent research published in 2018,^[4] taking the large amount of new photometric time-series data amassed since the publication of the original data into account, found evidence both for and against the exoplanet's existence. Although the planet's existence was not disproved, the case for its existence was now certainly weaker, and the authors stated that it "requires confirmation with an independent method."

The V391 Pegasi planetary system
Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b (unconfirmed)	>3.2±0.7 M_J	1.7±0.1	1170±44	0.00	—	—

References

^ Silvotti, R.; Randall, S. K.; Dhillon, V. S.; Marsh, T. R.; Savoury, C. D.; Schuh, S.; Fontaine, G.; Brassard, P. (December 2010). "V391 Peg: Identification of the two main pulsation modes from ULTRACAM u'g'r' amplitudes". Astronomische Nachrichten. 331: 1034–1037. arXiv:1005.2840. Bibcode:2010AN....331.1034S. doi:10.1002/asna.201011451. S2CID 119117121. Retrieved 14 February 2022.
^ ^a ^b ^c ^d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ Zacharias, N.; Finch, C. T.; Girard, T. M.; Henden, A.; Bartlett, J. L.; Monet, D. G.; Zacharias, M. I. (2012). "VizieR Online Data Catalog: UCAC4 Catalogue (Zacharias+, 2012)". VizieR On-line Data Catalog. Bibcode:2012yCat.1322....0Z.
^ ^a ^b ^c ^d ^e ^f ^g Silvotti, R.; Schuh, S.; Kim, S.L.; Lutz, R.; Reed, M.; Benatti, S.; Janulis, R.; Lanteri, L.; Østensen, R.; Marsh, T.R.; Dhillon, V.S. (March 2018), "The sdB pulsating star V391 Peg and its putative giant planet revisited after 13 years of time-series photometric data.", Astronomy & Astrophysics, 611: A85, arXiv:1711.10942, Bibcode:2018A&A...611A..85S, doi:10.1051/0004-6361/201731473, S2CID 119492634
^ Samus, N. N.; Durlevich, O. V.; et al. (2009), "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)", VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S, 1: B/gcvs, Bibcode:2009yCat....102025S
^ ^a ^b R. Østensen; J.-E. Solheim; U. Heber; R. Silvotti; et al. (2001), "Detection of pulsations in three subdwarf B stars", Astronomy and Astrophysics, 368 (1): 175–182, Bibcode:2001A&A...368..175O, doi:10.1051/0004-6361:20000488
^ ^a ^b ^c ^d Silvotti, R.; Schuh, S.; Janulis, R.; Solheim, J. -E.; Bernabei, S.; Østensen, R.; Oswalt, T. D.; Bruni, I.; Gualandi, R.; Bonanno, A.; Vauclair, G.; Reed, M.; Chen, C. -W.; Leibowitz, E.; Paparo, M.; Baran, A.; Charpinet, S.; Dolez, N.; Kawaler, S.; Kurtz, D.; Moskalik, P.; Riddle, R.; Zola, S. (2007), "A giant planet orbiting the 'extreme horizontal branch' star V391 Pegasi" (PDF), Nature, 449 (7159): 189–91, Bibcode:2007Natur.449..189S, doi:10.1038/nature06143, PMID 17851517, S2CID 4342338
^ Fortney, Jonathan (12 September 2007), "The one that got away", Nature, 449 (7159): 147–148, Bibcode:2007Natur.449..147F, doi:10.1038/449147a, PMID 17851500, S2CID 38288758

Sources

C. S. Jeffery (2005). "Pulsations in Subdwarf B Stars". Journal of Astrophysics and Astronomy. 26 (2–3): 261–271. Bibcode:2005JApA...26..261J. doi:10.1007/BF02702334. S2CID 13814916.

External links

"Notes for star V391 Peg". Extrasolar Planets Encyclopaedia. Archived from the original on November 6, 2007. Retrieved 2008-06-24.

Constellation of Pegasus

Stars

Bayer	α (Markab) β (Scheat) γ (Algenib) δ (Alpheratz) ε (Enif) ζ (Homam) η (Matar) θ (Biham) ι κ λ μ (Sadalbari) ν ξ ο π¹ π² ρ σ τ (Salm) υ (Alkarab) φ χ ψ
Flamsteed	1 2 3 4 5 7 9 11 12 13 14 15 16 17 18 19 20 21 23 25 28 30 31 32 33 34 35 36 37 38 39 40 41 45 51 (Helvetios) 52 55 56 57 58 59 60 61 63 64 65 66 67 69 70 71 72 73 74 75 76 77 78 79 80 82 83 85 86 87 23 Psc 34 Vul
Variable	R S U W Z RU RV RZ SV TW TY AG AQ AT AU AV AW BB BH BK BO BP BX BY DH DI DY EE EF EQ EZ GT GX HN HO HP HR HX II IK IM IP KT KU LL LO LS MS MT NV NZ OY PT V342 V343 V354 V363 V372 V376 V391
HR	19 49 8116 8219 8221 8231 8250 8257 8258 8274 8292 8325 8341 8348 8358 8359 8364 8372 8391 8397 8412 8415 8435 8441 8455 8456 8458 8460 8461 8466 8475 8482 8491 8503 8514 8543 8555 8564 8587 8604 8605 8608 8631 8638 8642 8737 8784 8788 8792 8824 8831 8833 8838 8839 8873 8922 8942 8953 8970 9039 9055 9078 9109
HD	434 204603 205011 205422 205603 206689 206793 208897 209709 210890 211076 213025 215549 215733 219196 219828 220288 220773 221170 221493 225292
Other	BD+14 4559 (Solaris) BD +17 4708 BD +28 4211 GD 246 Gl 829 Gl 880 HAT-P-8 NGC 8 NGC 18 NGC 30 PG 2131+066 PG 2303+243 PSR B2127+11C PSR B2303+30 Q2343-BX418 WASP-10 WASP-21 (Tangra) WASP-52 (Anadolu) WASP-59 WASP-60 (Morava) X2127+119 3C 454.3

Exoplanets	51 Pegasi b (Dimidium) WASP-10b BD+14 4559 b (Pirx) TOI-5678 b HD 209458 b HR 8799 b c d e

Star
clusters

Other	Balbinot 1 Messier 15

Nebulae

Other	Pease 1

Galaxies

NGC	1 2 9 14 15 16 22 23 26 41 42 52 7033 7034 7042 7043 7053 7056 7066 7068 7074 7085 7190 7217 7236 7237 7303 7312 7315 7317 7318 7319 7320 7320c 7331 7332 7427 7448 7454 7457 7466 7469 7479 7610 7619 7625 7673 7674 7678 7720 7726 7735 7741 7742 NGC 7752 NGC 7753 7767 7769 7773 7800 7814
Other	BX442 CTA-102 Einstein Cross Huchra's lens IC 5145 IC 5337 Markarian 335 Pegasus Dwarf Irregular Galaxy Pegasus Dwarf Spheroidal Galaxy Q2343-BX418

Galaxy clusters	Abell 2390 NGC 7331 Group Stephan's Quintet

Astronomical events	SN 1990U SN 2008ha SN 2013fs