UX Ari Research Articles

X-ray emission from UX ARIETIS - RS Canum Venaticorum systems as a class of coronal X-ray sources

We report the discovery of a new source of soft X-rays, H0324+28, observed with the HEAO 1 low-energy detectors, which we identify with the RS Canum Venaticorum system UX Ari. The source luminosity is 2.1 x 10/sup 31/ ergs s/sup -1/ (0.15--2.8 keV) and it has a temperature of 10/sup 7/ K. We briefly review the nature of RS Canum Venaticorum systems, discuss a possible model involving maintenance of a corona by extensive flaring, and suggest possible observational tests. We conclude that RS Canum Venaticorum systems form a new class of low-luminosity X-ray sources.

An X-ray outburst from the RS CVn binary HR1099

RS CANUM VENATICORUM systems are the most plentiful binary stars known, having a space density of at least 10−6 systems pc−3 (ref. 1). They are detached subgiants of class KO+F to G with orbital periods between 1 day and 2 weeks (ref. 1). Many exhibit wave-like distortions in V which sometimes migrate to earlier binary phase with periods of 10–20 yr. This phenomenon has been interpreted by Hall2 as resulting from extensive star spot activity on the surface of the cooler companion. Steady radio emission has been detected from several RS CVn systems with occasional flares involving an order of magnitude change in flux3–5. More recently, HEAO-A has detected soft X-ray emission (0.2–2.8 keV) from three of these systems HR1099, UX Ari and RS CVn itself6,7, with source luminosities of ∼1030 erg s−1. We report here the detection by the Copernicus 2.5–7.5 keV detector of a 3-h outburst from HR1099, coincident with a radio flare.

Copernicus observations of Ly-alpha and MG II emission from HR 1099 (V711 Tauri) and UX Ari

Ultraviolet observations of two RS CVn binaries obtained with Copernicus are described. High-resolution (0.05 A) U1 observations indicate that both HR 1099 and UX Ari display broad Ly-alpha emission. The Ly-alpha emission strength from HR 1099 is variable and seems to be correlated with orbital phase, while the UX Ari results indicate no significant variation. Moderate resolution (0.51 A) V2 scans of both systems show variable Mg II h and k emission-line profiles which usually matched the velocity of the more active star in each binary. Additionally, displaced emission components were seen at velocities of up to + or - 250 km/s, indicative of high-velocity gas motions. The radial velocities of these emission features from HR 1099 are marginally correlated with orbital phase. Highly active and variable chromospheric phenomena are found to be the most consistent explanation of these results.

1976-1977 photometry of UX Ari, HR 1099, and Lambda And

1976-1977 photometry of UX Ari, HR 1099, and Lambda And

Radio observations of the binary stars UX Ari and HR 1099.

The binary stars UX Arietis and HR 1099 have been observed at 2380 and 1400 MHz and UX Arietis was searched for at 430 MHz. A comparison of our observations with previous studies indicates that the radio spectra of these stars are typically flat from 1400 to 8085 MHz. A significant upper limit to the 430-MHz emission from UX Arietis was obtained, showing that the spectrum turns over between 1400 and 430 MHz. Circular polarization was detected in the 1400-MHz radiation from UX Arietis at a level of about 5%, and from HR 1099 at about 20%. It is suggested that the radio emission from these binaries is due to a gyrosynchrotron source which is optically thick to free--free absorption. Model-dependent source parameters are derived.

Variable radio emission from UX ARIETIS (HD 21242).

Variable radio emission from the spectroscopic binary UX Ari has been detected at frequencies of 2695, 5010, and 8085 MHz using the NRAO 91-m transit telescope and the NRAO four-element interferometer.