HP Lyrae

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HP Lyrae
HPLyrLightCurve.png
A blue band light curve for HP Lyrae, adapted from Wenzel (2013) [1]
Observation data
Epoch J2000       Equinox J2000
Constellation Lyra
Right ascension 19h 21m 39.066s [2]
Declination +39° 56′ 08.05″ [2]
Apparent magnitude  (V)10.43 [3] (10.2 - 10.8 [4] )
Characteristics
Spectral type A2-F2 Iab [4]
U−B color index +0.1 - +0.5 [4]
B−V color index +0.3 - +0.7 [4]
Variable type RV Tau [5]
Astrometry
Radial velocity (Rv)−107 [5]  km/s
Proper motion (μ)RA: −2.485±0.038 [6]   mas/yr
Dec.: −5.500±0.047 [6]   mas/yr
Parallax (π)0.0822 ± 0.0242  mas [6]
Distance 6,700±380 [7]   pc
Absolute magnitude  (MV)−4.5 [4]
Orbit [7]
Period (P)1,631 days
Eccentricity (e)0.17
Argument of periastron (ω)
(secondary)		5.5°
Semi-amplitude (K1)
(primary)		7.7 km/s
Details [5]
Mass 0.6 [7]   M☉
Radius 60 [7]   R☉
Luminosity 3,900±400 [7]   L☉
Surface gravity (log g)1.0  cgs
Temperature 5,900 [7]   K
Metallicity [Fe/H]−1.0  dex
B
Mass 0.5 - 0.6 [7]   M☉
Other designations
HP  Lyrae, TYC  3138-54-1, ASAS  J192139+3956.1, IRAS  19199+3950, 2MASS  J19213906+3956080, AAVSO  1918+39
Database references
SIMBAD data

HP Lyrae (HP Lyr) is a variable star in the constellation Lyra, with a visual magnitude varying between 10.2 and 10.8. It is likely to be an RV Tauri variable, an unstable post-AGB star losing mass before becoming a white dwarf.

Contents

Discovery

HP Lyr was first reported to be variable in 1935 by Otto Morgenroth of the Sonneberg Observatory. The range was given as 9.5 - 10.5 and the variability type only as long-period. [8] In 1961, it was formally designated as a β Lyr eclipsing variable with two A type supergiants in a close orbit producing smooth continuous variations with alternating minima of different depths. The period was given as 140.75 days, covering two maxima, and both a deep primary minimum and a slightly less deep secondary minimum. [9]

In 2001 a request was made for observations of HP Lyr [10] and shortly after it was reported that HP Lyr was likely to be an RV Tauri variable rather than an eclipsing binary. [11] This was confirmed with a more detailed study published in 2002. [4] Some authors still maintain that the spectral type and nature of variation mean HP Lyr is more likely to be an eclipsing variable. [12]

Variability

HP Lyr varies by about 0.5 magnitude over a "halfperiod" of 68.4 days. [7] The formal period, defined for an RV Tauri variable as being from deep minimum to deep minimum is twice that length. Its spectrum changes from A2-3 at maximum to F2 at the deepest minima. The radial velocity changes are typical for the pulsations of an RV Tauri variable, but not compatible with a binary orbit. The spectral type and colour indicated that it was likely to be the hottest known RV Tauri star. [4]

Until 1960, the period of HP Lyr was very consistent at 140.75 days. Since then it was observed to reduce to below 140 days, probably quite suddenly. A survey of historic photography including the star showed that the period changed in 1962 or 1963, taking no more than four cycles to reach a new value of 138.66 days. [1]

Properties

A 2005 study of the elemental abundances of RV Tauri stars calculated that HP Lyr had a temperature around 6,300  K and typical abundances for an RV Tauri variable. It also revealed that the abundances were altered by dust-gas separation in circumstellar material. [5] HP Lyr has been included in a catalog of confirmed post-AGB stars, highly evolved and on its way to becoming a white dwarf. [13] In 2017, the temperature was calculated to be 5,900 K, still one of the hottest known RV Tau variables. [7]

The distance is uncertain, although large. Gaia Data Release 2 contains a parallax indicating a distance around 12,000  pc . [6] Using luminosities derived from a period-luminosity-colour relationship, together with interstellar extinctions, gives a distance around 6,700 K. From the radius and effective temperature, the radius is calculated to be 60 R☉. [7]

HP Lyrae is a post-AGB star, one that has completed its evolution along the asymptotic giant branch (AGB) and is now rapidly shedding its outer layers prior to becoming a white dwarf. During this process it becomes hotter and is crossing the instability strip which causes it to become unstable and pulsate. [7]

Binary

Many RV Tauri stars are found to be in binary systems, and HP Lyrae has an invisible companion in a 1,631  d orbit. Its properties are not known, but the mass is estimated to be a little under 0.6 M☉, leaving open the possibility that it is a white dwarf. [7]

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References

  1. 1 2 Wenzel, W. (2013). "HP Lyrae – the sudden period decrease". Minutes on Variable Stars (MVS13–01).
  2. 1 2 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
  3. ↑ Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H.
  4. 1 2 3 4 5 6 7 Graczyk, D.; Mikolajewski, M.; Leedjarv, L.; Frackowiak, S. M.; Osiwala, J. P.; Puss, A.; Tomov, T. (2002). "HP Lyr - Possibly the Hottest RV Tau Type Object". Acta Astronomica. 52: 293–304. arXiv: astro-ph/0210448 . Bibcode:2002AcA....52..293G.
  5. 1 2 3 4 Giridhar, Sunetra; Lambert, David L.; Reddy, Bacham E.; Gonzalez, Guillermo; Yong, David (2005). "Abundance Analyses of Field RV Tauri Stars. VI. An Extended Sample". The Astrophysical Journal. 627 (1): 432–445. arXiv: astro-ph/0503344 . Bibcode:2005ApJ...627..432G. doi:10.1086/430265. S2CID   18053310.
  6. 1 2 3 4 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.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 Manick, Rajeev; Van Winckel, Hans; Kamath, Devika; Hillen, Michel; Escorza, Ana (2017). "Establishing binarity amongst Galactic RV Tauri stars with a disc⋆". Astronomy and Astrophysics. 597: A129. arXiv: 1610.00506 . Bibcode:2017A&A...597A.129M. doi:10.1051/0004-6361/201629125. S2CID   119242786.
  8. ↑ Morgenroth, O. (1935). "23 neue Veränderliche". Astronomische Nachrichten. 255 (23): 425–428. Bibcode:1935AN....255..425M. doi:10.1002/asna.19352552303.
  9. ↑ Wenzel, W. (1961). "Two Variables of Beta Lyrae Type with Long Periods". Information Bulletin on Variable Stars. 1: 1. Bibcode:1961IBVS....1....1W.
  10. ↑ Meyer, R. (2001). "Beobachtungsaufruf: HP Lyr". BAV Rundbrief. 50: 5. Bibcode:2001BAVSR..50....5M.
  11. ↑ Hassforther, B. (2002). "HP Lyrae ist wahrscheinlich ein RV-Tauri-Stern". BAV Rundbrief. 51: 182. Bibcode:2002BAVSR..51..182H.
  12. ↑ Alfonso-Garzón, J.; Domingo, A.; Mas-Hesse, J. M.; Giménez, A. (2012). "The first INTEGRAL-OMC catalogue of optically variable sources". Astronomy & Astrophysics. 1210: A79. arXiv: 1210.0821 . Bibcode:2012A&A...548A..79A. doi:10.1051/0004-6361/201220095. S2CID   118428054.
  13. ↑ Szczerba, R.; Siódmiak, N.; Stasińska, G.; Borkowski, J. (2007). "An evolutionary catalogue of galactic post-AGB and related objects". Astronomy and Astrophysics. 469 (2): 799–806. arXiv: astro-ph/0703717 . Bibcode:2007A&A...469..799S. doi:10.1051/0004-6361:20067035. S2CID   16505186.
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