HP Lyrae
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.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Lyra |
| Right ascension | 19h 21m 39.066s[1] |
| Declination | +39° 56′ 08.05″[1] |
| Apparent magnitude (V) | 10.43[2] (10.2 - 10.8[3]) |
| Characteristics | |
| Spectral type | A2-F2 Iab[3] |
| U−B color index | +0.1 - +0.5[3] |
| B−V color index | +0.3 - +0.7[3] |
| Variable type | RV Tau[4] |
| Astrometry | |
| Radial velocity (Rv) | −107[4] km/s |
| Proper motion (μ) | RA: −2.485±0.038[5] mas/yr Dec.: −5.500±0.047[5] mas/yr |
| Parallax (π) | 0.0822 ± 0.0242[5] mas |
| Distance | 6,700±380[6] pc |
| Absolute magnitude (MV) | −4.5[3] |
| Orbit[6] | |
| 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[4] | |
| Mass | 0.6[6] M☉ |
| Radius | 60[6] R☉ |
| Luminosity | 3,900±400[6] L☉ |
| Surface gravity (log g) | 1.0 cgs |
| Temperature | 5,900[6] K |
| Metallicity [Fe/H] | −1.0 dex |
| B | |
| Mass | 0.5 - 0.6[6] M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
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.[7] 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.[8]
In 2001 a request was made for observations of HP Lyr[9] and shortly after it was reported that HP Lyr was likely to be an RV Tauri variable rather than an eclipsing binary.[10] This was confirmed with a more detailed study published in 2002. [3] Some authors still maintain that the spectral type and nature of variation mean HP Lyr is more likely to be an eclipsing variable.[11]
Variability
HP Lyr varies by about 0.5 magnitude over a "halfperiod" of 68.4 days.[6] 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.[3]
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.[12]
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.[4] 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.[6]
The distance is uncertain, although large. Gaia Data Release 2 contains a parallax indicating a distance around 12,000 pc.[5] 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☉.[6]
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.[6]
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.[6]
References
- Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally Published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.
- 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.
- 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.
- 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.
- 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.
- 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.
- Morgenroth, O. (1935). "23 neue Veränderliche". Astronomische Nachrichten. 255 (23): 425–428. Bibcode:1935AN....255..425M. doi:10.1002/asna.19352552303.
- Wenzel, W. (1961). "Two Variables of Beta Lyrae Type with Long Periods". Information Bulletin on Variable Stars. 1: 1. Bibcode:1961IBVS....1....1W.
- Meyer, R. (2001). "Beobachtungsaufruf: HP Lyr". BAV Rundbrief. 50: 5. Bibcode:2001BAVSR..50....5M.
- Hassforther, B. (2002). "HP Lyrae ist wahrscheinlich ein RV-Tauri-Stern". BAV Rundbrief. 51: 182. Bibcode:2002BAVSR..51..182H.
- 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.
- Wenzel, W. (2013). "HP Lyrae – the sudden period decrease". Minutes on Variable Stars (MVS13–01).
- 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.