* Astronomy

Blobrana · L

RE: SS Cygni

Blobrana · L

SS Cygni is a variable star in the northern constellation Cygnus (the Swan). It is classified as a dwarf nova, meaning that it undergoes frequent and regular brightness outbursts - every 7 or 8 weeks in the case of this much-observed example. SS Cygni is often classified as a U Geminorum type dwarf nova. However, the maxima of SS Cygni are typically brighter than those of U Gem, rising from 12th magnitude to 8th magnitude for, typically, 1-2 days.
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Blobrana · L

The cataclysmic variable star SS Cygni is in outburst.

Date of Outburst: 15th March, 2010
Magnitude: 7.7 - 12.4 V
Period: 49.5 days
Satellite Period: 0.27513 days
Type: UGSS

Position(2000): RA=21 42 42.79, Dec=+43°35'09.9"

Blobrana · L

Title: The Accreting White Dwarf in SS Cygni Revealed
Authors: Edward Sion, Patrick Godon, Janine Myzcka, William Blair

We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far Ultraviolet Spectroscopic Explorer FUSE) analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. In our synthetic spectral analysis, we have used SS Cygni's accurate HST FGS parallax giving d = 166pc, a newly determined mass for the accreting white dwarf (Bitner et al. 2007) of Mwd=0.81Msun (lower than the previous, widely used 1.2 Msun) and the reddening E_{B-V} values 0.04 (Verbunt 1987; La Dous 1991) and 0.07 (Bruch and Engel 1994) derived from the 2175A absorption feature in the IUE LWP spectra. From the best-fit model solutions to the combined HST + FUSE spectral energy distribution, we find that the white dwarf is reaching a temperature Teff of 45-55,000K in quiescence, assuming Log(g)= 8.3 with a solar composition accreted atmosphere. The exact temperature of the WD depends on the reddening assumed and on the inclusion of a quiescent low mass accretion rate accretion disk. Accretion disk models alone fit badly in the FUSE range while, and if we take the distance to be a free parameter, the only accretion disk model which fits well is for a discordant distance of at least several hundred pc and an accretion rate (1.E-8 Msun/yr which is unacceptably high for a dwarf nova in quiescence. We discuss the implications of the white dwarf's temperature on the time-averaged accretion rate and long term compressional heating models.

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Blobrana · L

Title: Interpreting a Dwarf Nova Eruption as Magnetic Flare Activity
Authors: Noam Soker (Technion), Saeqa Dil Vrtilek (CfA)
(Version v2)

We suggest that the radio emission from the dwarf nova SS Cyg during outburst comes from magnetic activity that formed a corona (similar to coronae found in magnetically active stars), rather than from jets. We base our claim on the recent results of Laor & Behar, who found that when the ratio between radio and X-ray flux of accretion disks in radio-quiet quasars is as in active stars, Lr/Lx=10^{-5}, then most of the radio emission comes from coronae. Using observations from the literature we find that for SS Cyg during outburst Lr/Lx<10^{-5}. This does not mean jets are not launched during outbursts. On the contrary, if the magnetic activity in erupting accreting disks is similar to that in stars, then mass ejection, e.g., as in coronal mass ejection, is expected. Hence magnetic flares similar to those in active stars might be the main mechanism for launching jets in a variety of systems, from young stellar objects to massive black holes.

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Blobrana · L

The cataclysmic variable star SS Cygni is in outburst.

Date of Outburst: 23rd October, 2008
Magnitude: 7.7 - 12.4 V
Period: 49.5 days
Satellite Period: 0.27513 days
Type: UGSS

Position(2000): RA=21h42m42.80s, Dec=+43°35'09.9"

Blobrana · L

SS Cygni in outburst

The variable star reaches 9th magnitude and should get brighter.

Source

Position(J2000): RA 21h 42m 42.66s, Dec +43° 35' 9.48"

-- Edited by Blobrana at 20:09, 2008-08-27

Blobrana · L

Astronomers have discovered a previously unexpected astronomical phenomenon a radio jet in a star system where none had been expected which suggests that all stars and black holes feed in the same way.
Astronomers from Southampton and Manchester Universities and the National Radio Astronomy Observatory in Virginia, USA, in collaboration with the American Association of Variable Star Observers and other amateur astronomers (including those of the British Astronomical Association), were monitoring the outburst of the dwarf nova SS Cygnus when they made their discovery. The research paper will be published by the journal Science on 6 June.

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Blobrana · L

Title: A Search for SS Cyg Outburst Predictors
Authors: A. Price, A. A. Henden, G. Foster, V. Petriew, R. Huziak, R. James, M. D. Koppelman, J. Blackwell, D. Boyd, S. Brady, Lewis M. Cook, T. Crawford, B. Dillon, B. L. Gary, B. Goff, K. Graham, K. Holland, J. Jones, R. Miles, D. Starkey, S. Robinson, T. Vanmunster, G. Walker

We report null results on a two year photometric search for outburst predictors in SS Cyg. Observations in Johnson V and Cousins I were obtained almost daily for multiple hours per night for two observing seasons. The accumulated data are put through various statistical and visual analysis techniques but fails to detect any outburst predictors. However, analysis of 102 years of AAVSO archival visual data led to the detection of a correlation between a long term quasi-periodic feature at around 1,000-2,000 days in length and an increase in outburst rate.

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Blobrana · L

Title: The dwarf nova SS Cygni: what is wrong?
Authors: Matthias R. Schreiber, Jean-Pierre Lasota

Since using the Fine Guiding Sensor (FGS) on the Hubble Space Telescope (HST) the distance to SS Cyg has been measured to be 166 ±12 pc, it became apparent that at this distance the disc instability model fails to explain the absolute magnitude during outburst. It remained, however, an open question whether the model or the distance has to be revised. Recent observations led to a revision of the system parameters of SS Cyg and seem to be consistent with a distance of d\gta 140 pc. We re-discuss the problem taking into account the new binary and stellar parameter measured for SS Cyg. We confront not only the observations with the predictions of the disc instability model but also compare SS Cyg with other dwarf novae and nova-like systems. We assume the disc during outburst to be in a quasi stationary state and use the black-body approximation to estimate the accretion rate during outburst as a function of distance. Using the analysis of the long term light curve we determine the mean mass transfer rate of SS Cyg as a function of distance and compare the result with mass transfer rates derived for other dwarf novae and nova-like systems. At a distance of d\gta 140 pc, both the accretion rate during outburst as well as the mean mass transfer rate of SS Cyg contradict the disc instability model. More important, at such distances we find the mean mass transfer rate of SS Cyg to be higher or comparable to those derived for nova-like systems. Our findings show that a distance to SS Cyg \gta 140 pc contradicts the main concepts developed for accretion discs in cataclysmic variables during the last 30 years. Either our current picture of disc accretion in these systems must be revised or the distance to SS Cyg is ~ 100 pc.

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