Brown dwarf at BL Cam, SX Phe variable (and binary too)?

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Brown dwarf at BL Cam, SX Phe variable (and binary too)?

Post by Edasich on 19th April 2010, 4:32 am

Sounds cool. I like timing variations like this. Laughing

The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system

Short-period high-amplitude pulsating stars of Population I ($\delta$ Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. aims heading (mandatory) We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses. methods heading (mandatory) An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. results heading (mandatory) In addition to a positive (161 $\pm$ 3) x 10$^{-9}$ yr$^{-1}$ secular relative increase in the main pulsation period of BL Cam, we detected in the O-C data short- (144.2 d) and long-term ($\sim$ 3400 d) variations, both incompatible with a scenario of stellar evolution. conclusions heading (mandatory) Interpreted as a light travel-time effect, the short-term O-C variation is indicative of a massive stellar component (0.46 to 1 M$_{\sun}$) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O-C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably a brown dwarf star ($\geq$ 0.03 \ M$_{\sun}$), orbiting in 3400 d at a distance of 4.5 AU from the primary.

Notice that hints of the low-mass companions are also reported in this 2008 paper of Fu et alii. Where eccentricity of outer companion is also provided.

Variability Study of the SX Phoenicis Star BL Camelopardalis

They determined more than 100new times of maximum light and gave dP/Pdt = 1.17(0.03) 10−7 yr−1, showing that the star has acompanion in a rather eccentric orbit (e = 0.7 0.2) with a period of 10.5(0.2) yr.

dM star
dM star

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