* Astronomy

Blobrana · L

RE: U Geminorum

Blobrana · L

U Geminorum is in outburst

Outburst Date: 30th December, 2011
Magnitude: 8.2 - 14.9 V
Outburst Period: 105.2 days
Orbital period of the satellite: 0.1769061 days
Type: UGSS

Position (J2000): R.A. 07 55 05.24 | Dec. +22° 00' 05.1''

Blobrana · L

U Geminorum is in outburst

Outburst Date: 24th November, 2011
Magnitude: 8.2 - 14.9 V
Outburst Period: 105.2 days
Orbital period of the satellite: 0.1769061 days
Type: UGSS

Position(2000): RA=07 55 05.20, Dec=+22°00 05.0"

Blobrana · L

Google earth file: U Geminorum.kmz (1kb, kmz)

Blobrana · L

U Geminorum is in outburst

Outburst Date: 23rd March, 2011
Magnitude: 8.2 - 14.9 V
Outburst Period: 105.2 days
Orbital period of the satellite: 0.176906 days
Type: UGSS

Position(2000): RA=07 55 05.20, Dec=+22°00 05.0"

Blobrana · L

U Geminorum has brightened

Outburst Date: 25th September, 2008
Magnitude: 8.2 - 14.9 V
Outburst Period: 105.2 days
Orbital period of the satellite: 0.176906 days
Type: UGSS

Position(2000): RA=07h55m05.20s, Dec=+22°00 05.0"

-- Edited by Blobrana at 22:49, 2008-09-25

Blobrana · L

Title: U Geminorum: a test case for orbital parameters determination
Authors: J. Echevarria (1), E. de la Fuente (2), R. Costero (1) ((1) IA UNAM, Mexico, (2) Departamento de Fisica, CUCEI, Universidad de Guadalajara, Mexico)

High-resolution spectroscopy of U Gem was obtained during quiescence. We did not find a hot spot or gas stream around the outer boundaries of the accretion disk. Instead, we detected a strong narrow emission near the location of the secondary star. We measured the radial velocity curve from the wings of the double-peaked H$\alpha$ emission line, and obtained a semi-amplitude value that is in excellent agreement with the obtained from observations in the ultraviolet spectral region by Sion et al. (1998). We present also a new method to obtain K_2, which enhances the detection of absorption or emission features arising in the late-type companion. Our results are compared with published values derived from the near-infrared NaI line doublet. From a comparison of the TiO band with those of late type M stars, we find that a best fit is obtained for a M6V star, contributing 5 percent of the total light at that spectral region. Assuming that the radial velocity semi-amplitudes reflect accurately the motion of the binary components, then from our results: K_em = 107+/-2 km/s; K_abs = 310+/-5 km/s, and using the inclination angle given by Zhang & Robinson(1987); i = 69.7+/-0.7, the system parameters become: M_WD = 1.20+/-0.05 M_sun,; M_RD = 0.42+/-0.04 M_sun; and a = 1.55+/- 0.02 R_sun. Based on the separation of the double emission peaks, we calculate an outer disk radius of R_out/a ~0.61, close to the distance of the inner Lagrangian point L_1/a~0.63. Therefore we suggest that, at the time of observations, the accretion disk was filling the Roche-Lobe of the primary, and that the matter leaving the L_1 point was colliding with the disc directly, producing the hot spot at this location.

Read more (387kb, PDF)

Blobrana · L

Title: X-ray Spectral Variations of U Gem from Quiescence to Outburst
Authors: T. Guver, C. Uluyazi, M.T. Ozkan, E. Gogus

In this paper researchers report the discovery of a high energy component of the X-ray spectra of U Geminorum, which can be observed while the source is in outburst. They used Chandra and XMM-Newton observations to compare the quiescence and outburst X-ray spectra of the source. The additional component may be the result of the reflection of X-rays emitted from an optically thin plasma close to the white dwarf, from the optically thick boundary layer during the outburst.
Another possible explanation is that some magnetically channelled accretion may occur onto the equatorial belt of the primary causing shocks similar to the ones in the intermediate polars as it was suggested by Warner and Woudt 2002. The researchers have also found a timing structure at about 73 mHz (~13.7 s.) in the RXTE observation, resembling dwarf novae oscillations (DNOs).

Read more (215kb, PDF)