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 $\sim$ 3400 d at a distance of 4.5 AU from the primary.Comment: 7 pages, 5 figures, accepted for publication in A&

B.R.N.O. Contributions #38 Times of minima

This paper presents observations of eclipsing binaries acquired by members and cooperating observers of the Variable Star and Exoplanet Section of Czech Astronomical Society (B.R.N.O. observing project). Paper contains 3417 times of minima for 969 objects. It was obtained by 80 observers during 2011 – 2013 period. Some neglected southern eclipsing binaries and newly discovered stars by the observers of project B.R.N.O. are included in the list. New accurate ephemerides have been found for 447 binary systems. Time of primary minimum of long period variable eps Aur is presented as wellFil: Hoňková, K. Variable Star and Exoplanet Section of Czech Astronomical Society; República Checa. Observatory and Planetarium of Johann Palisa; República ChecaFil: Juryšek, J. Variable Star and Exoplanet Section of Czech Astronomical Society; República Checa. Observatory and Planetarium of Johann Palisa; República ChecaFil: Lehký, M. Variable Star and Exoplanet Section of Czech Astronomical Society; República Checa. Astronomical Society at Hradec Kralove; República ChecaFil: Šmelcer, L. Variable Star and Exoplanet Section of Czech Astronomical Society; República Checa. Valašské Meziříčí Observatory; República ChecaFil: Trnka, J. Variable Star and Exoplanet Section of Czech Astronomical Society; República Checa. City Observatory Slaný; República ChecaFil: Colazo, C. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Estación Astrofísica Bosque Alegre; ArgentinaFil: Guzzo, P. Estación Astrofísica Bosque Alegre; ArgentinaFil: Mina, Federico Daniel. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Quinones, C. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Taormina, M. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Melia, R. Observatorio Remoto Bosque Alegre; ArgentinaFil: Schneiter, Ernesto Matías. Estación Astrofísica Bosque Alegre; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Scavuzzo, Alan Martin. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Marcionni, M. Estación Astrofísica Bosque Alegre; ArgentinaFil: Tapia, L. Estación Astrofísica Bosque Alegre; ArgentinaFil: Fasseta, G. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Suarez, N. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Vilášek, M. Observatory and Planetarium of Johann Palisa; República ChecaFil: Rozehnal, J.. Štefánik Observatory; República ChecaFil: Kalisch, T. Variable Star and Exoplanet Section of Czech Astronomical Society; República Checa. Observatory and Planetarium of Johann Palisa; República ChecaFil: Lang, K.. Klokkerholm; DinamarcaFil: Gorková, S. ALTAN.Observatory; República ChecaFil: Novysedlák, R. Námestie sv. Martina; EslovaquiaFil: Salvaggio, F. Gruppo Astrofili Catanesi; ItaliaFil: Smyčka, T. Variable Star and Exoplanet Section of Czech Astronomical Society; República Checa. City Observatory Slaný; República ChecaFil: Spurný, M. Nejdlova 16; República ChecaFil: Wikander, T. Ornäs Backyard; República ChecaFil: Mravik, J. Slobodana Jajića 16; República ChecaFil: Šuchaň, J. Kraskova 12; EslovaquiaFil: Čaloud, J.. V Dolině 211; República Chec

The field high-amplitude SX Phe variable BL Cam: Results from a multisite photometric campaign: II. Evidence of a binary - Possibly triple - System

Context.Short-period high-amplitude pulsating stars of Population I (d 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.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.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. In addition to a positive (161 ± 3) × 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 (~3400 d) variations, both incompatible with a scenario of stellar evolution. Conclusions. 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?) 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 (=0.03 M?), orbiting in ~3400 d at a distance of 4.5 AU from the primary. © ESO, 2010