VY Aquarii

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Double star
VY Aquarii
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Aquarius
Right ascension 21 h 12 m 9.25 s
declination -08 ° 49 ′ 36.8 ″
Apparent brightness 10.0 to 17.5 mag
Typing
rel. Brightness
(G-band) 		(16,865 ± 0.0267) mag
rel. Brightness
(J-band) 		(15,278 ± 0.052) mag
B − V color index −4.0 
Spectral class pec (basement)
Variable star type UQSU 
Astrometry
parallax (7.236 ± 0.136)  mas
distance 450 ± 8.5  ly
138.2 ± 2.6  pc  
Proper movement 
Rec. Share: (49.7 ± 8.3)  mas / a
Dec. portion: (−31.4 ± 8.5)  mas / a
Physical Properties
Rotation time 90.85 min
Other names
and catalog entries
2MASS catalog 2MASS J21120925-0849367 [1]
Other names VY Aqr, 1RXS J211208.1-085004, 2RXS J211208.2-085007, 6dFGS g2112092-084934, AAVSO 2106-09, APOP 48421 + 0011153, AllWISE J211209.27-084937.2, CMC15 J211209.2, CSS 084936, GALEX J211209.2-084936, GSC2.3 SC2T011153, N Aqr 1907, Nova Aqr 1907, PM J21121-0849, Ross 88, SBC9 2427, SDSS J211209.26-084936.9, UCAC4 406-136414, USNO-A2.0 0750-20686374, USNO-B1.0 0811-0669228, WISE J211209.27-084937.1, XPM 162-0957324

Template: Infobox Star / Maintenance / MagGTemplate: Infobox Star / Maintenance / MagJ

VY Aquarii also VY Aqr is a dwarf nova , and thus a cataclysmically variable binary star system , which was discovered in 1907 by Frank Elmore Ross .

Most of the time VY Aquarii at rest at a visual luminosity of 17 m to 17.5 m . After outbreaks of around ninth magnitude in 1907, 1962 and 1973, the system was classified as a recurrent nova based on an empirical rule of thumb according to which dwarf novae with outbreaks of smaller amplitude (<5 mag) and greater frequency (weeks to months) were classified as such .

Further investigation of observational data obtained both during periods of rest and during eruptions underscored the great similarity of the star to the well-understood dwarf novae such as WZ Sagittae . The long-term visual and photographic recordings show two types of outbursts, which differ in brightness and time scale by a factor of 5.

Photometric recordings during a long outbreak in 1986 showed a large amplitude modulation (called a superhump ) lasting 92.7 (or possibly 99.1) minutes, which slowly decreased during the outbreak. A wave at the transition to the rest light curve indicated a period in the range of 80-120 minutes, which could correspond to the orbital period of a binary component. These are usually signatures of SU Ursae Majoris stars , a subclass of the dwarf novae. The superhumps observed in SU-UMa stars appear to have a similar degree of period instability. A physically more significant indication of this is the period-luminosity relationship : the periods decrease in the early phase by at least 0.64 ± 0.10%. This is an entirely explainable decrease if one assumes with the assumed model for the formation of superhumps that the maximum brightness occurs at the outermost edge of an accretion disk .

The carefully observed eruption of WZ Sagittae from 1978, which had previously been classified as a recurrent nova for the same reasons, made it clear, however, that this was demonstrably a dwarf nova, since the cause of the eruption is a bistable state of the accretion disc, which occurs when the mass accretion rate falls below a critical value. During the dwarf nova outbreak, when a critical density is exceeded, there is a sudden increase in viscosity , as a result of which the matter that has accumulated in the accretion disk is increasingly transferred to the white dwarf .

Joseph Patterson et al. describe a multitude of aspects that have been gathered over 12 years of observation by VY Aquarii. The long-term eruption history , spectroscopy and photometry , during the dormant phase, and high-speed photometry, of the 1986 eruption were examined. This data shows that VY Aquarii is undoubtedly a dwarf nova and represents the comprehensive history of the development of superhumps in the light curve of a dwarf nova.

History of VY Aquarii

Originally this variable was considered a recurring nova, but in the meantime the classification of VY Aquarii has fundamentally changed. At first only the discovery outbreak with a brightness of 8.4 m from 1907 and the maximum from 1962 were known. However, after examination of surveys and intensive visual monitoring by amateur observers in recent times, a number of other outbreaks were found, which occurred at least in 1929, 1934, 1942, 1958, 1973, 1983 and 1986. Long-term visual and photographic observations show that VY Aquarii has two types of outbursts that correspond to the dichotomy of SU-Ursae-Majoris stars , namely short and weak with a "normal maxima" and long and bright with a "super maxima".

VY Aquarii was also active in the years 1939, 1940, and 1964 to 67. From this eruption behavior and from the physical properties of the accretion disk, it was finally concluded that VY Aquarii is “only” a dwarf nova. As the different bright and long maxima suggested, the discovery of superhumps revealed that the variable is one of the SU-UMa stars . Also in 1988 and 1989 u. a. by observers of the Berlin Working Group for Changeable Stars e. V. (BAV) Maxima are tracked by VY Aquarii. While the short maximum in August 1989 could unfortunately only be covered insufficiently, the observations of the super maximum from September of the same year allow the creation of a light curve. This super maximum was very similar to that presented by UV Persei . This is especially true for the rapid increase in brightness and the speed at which it falls. What is missing in the light curve due to a lack of observations is a very narrow intermediate minimum that occurs in the decrease in brightness. This phenomenon has often been observed in the past both in VY Aquarii itself and in the similar dwarf novae AL Coma Berenices , V592 Hercules , WZ Sagittae and RZ Leonis (the latter two stars were also once considered to be recurrent novae, V592 Her gar as a classic nova ). Since the origin of this phenomenon has not yet been finally clarified, the monitoring of VY Aquarii and his fellow species is an extremely important matter.

See also

Individual evidence

  1. ↑ a b c d e f g VY Aqr. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed April 19, 2019 .
  2. ↑ a b c d VY Aqr. In: VSX. AAVSO , accessed April 19, 2019 .
  3. ↑ a b c Patterson, J .; McGraw, JT; Coleman, L .; Africano, JL: A photometric study of the dwarf nova WZ Sagittae in outburst . In: Astrophysical Journal, Part 1, vol. 248, Sept. 15, 1981, p. 1067-1075. . 1981. bibcode : 1981ApJ ... 248.1067P . doi : 10.1086 / 159236 .
  4. ↑ Gilliland RL, Kemper, E .: WZ Sagittae - Recent observations leading to a model for superhump phenomena . In: Astrophysical Journal, Part 1, vol. 236, Mar. 15, 1980, p. 854-861. . 1980. bibcode : 1980ApJ ... 236..854G . doi : 10.1086 / 157810 .
  5. ^ A b Joseph Patterson, Howard E. Bond, Albert D. Grauer, Allen W. Shafter, and Janet A. Mattei: SUPERHUMPS IN VY AQUARII . In: Publications of the Astronomical Society of the Pacific, Volume 105, Number 683 . 1993. doi : 10.1086 / 133128 .
  6. ^ Ross, Frank E.: New variable stars . In: Astronomical Journal, vol. 36, eat. 856, p. 122-124 . 1926. bibcode : 1926AJ ..... 36..122R . doi : 10.1086 / 104698 .
  7. ↑ Strohmeier, W .: New Eruption of Nova VY Aquarii . In: Information Bulletin on Variable Stars, No. 15, # 1 . 1962. bibcode : 1962IBVS ... 15 .... 1S .
  8. ↑ a b Webbink, Ronald F .; Livio, Mario; Truran, James W .; Orio, Marina: The nature of the recurrent novae . In: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 314, March 15, 1987, p. 653-672 . 1987. bibcode : 1987ApJ ... 314..653W . doi : 10.1086 / 165095 .
  9. ↑ a b c Korth, S .: The outbreak behavior of selected cataclysmic binary stars in the years 1987-1989 . In: BAV-Mitteilungen No. 54 . 1990.