Variable stars of Gaia

Gaia gives its first results and speaks much Italian. It’s a confirmation of the leading role that the community has in this national astrophysics mission of ESA.
In two recent press release on the website of the ESA, a team of astrophysicists presented the first results of the data analysis of commissioning of the Gaia satellite, authors of the first scientific survey of Gaia Alerts publication in the journal Monthly Notices of the Royal Astronomical Society.
In March 2015, a first draft of photometry obtained from Gaia during commissioning has been analyzed by the team of Gaia Data Processing and Analysis Consortium (DPAC) in charge of studying the variables sources from the satellite (the Coordination Unit 7 – CU7, with Based in Geneva). The international team of DPAC deals with task such as identifying and characterizing the variables RR Lyrae and Cepheid observed by Gaia.


Credit: ESA/Gaia/DPAC/CU5/CU7

“The data variables sources observed by Gaia in the Large Magellanic Cloud were analyzed with the pipeline developed by our team,” says Silvio Leccia, from Osservatorio di Capodimonte that developed the code in Java used for this analysis. “The results we have amply repaid for all the effort of these years of hard work on the project,” adds Vincenzo Ripepi, researcher at the Observatory, “we have identified more than 800 RR Lyrae variables, including several hundred that are new discoveries of Gaia.”
“We also managed to find some Cepheids”, adds Gisella Clementini “the few and weak included in this first data processing Gaia containing predominantly fainter sources than mag 17.5.” “Cepheids and RR Lyrae calibrators are fundamental cosmic distance scale, the set of methods that astronomers use to measure distances of celestial objects. These measures take place in successive stages, starting with the parallax of the nearest objects that Gaia will measure with extreme accuracy, up to, through indirect methods and so-called “standard candles” to the most distant objects (over 100 Megaparsec, about 326 million light years) from which distance depends on the measurement of the Hubble constant, a fundamental parameter for cosmological theories. ”
“Gaia observes the whole sky over again,” says Giuseppe Altavilla INAF Observatory of Bologna. “From the beginning it was decided to use these skills to identify transient phenomena: Supernovae, events Microlensing, Novae, asteroids, cataclysmic variables, planetary transits, to name a few, not to mention the possibility of any rare, exotic and unknown phenomena. And why in 2010 was born on Gaia Science Alerts (GSA) Programme. And now we start receiving the first results. ”
The first article of the GSA collaboration has been accepted for publication in (“Total eclipse of the heart: The AM CVn Gaia14aae / ASSASN-14cn”, Campbell et al. 2015), which was attended by several Italian researchers (Giuseppe Altavilla, Gisella Clementini, Roberto Gualandi, Giuseppe Leto, Lina Tomasella and Massimo Turatto).


Credit: ESA/Gaia/DPAC/CU5/CU7

G-band light curves of RR Lyrae stars in the Large Magellanic Cloud observed by Gaia during the EPSL scanning. Right panels: I-band light curves obtained for the same stars by the OGLE IV survey. All light curves cover a 1.5 pulsation cycle.

“Gaia14aae, identified by Gaia in the summer of 2014, appeared to be suddenly one of the most interesting transients observed by the satellite, and it was immediately observed by ground telescopes including the Cassini telescope in Loiano and Copernicus in Asiago”, says Giuseppe Altavilla.
Gaia14aae is a rare example of a cataclysmic variable of type AM Canum Venaticorum (AM CVn) in a binary system consisting of a compact star (the variable itself) which draws material from a companion. The two stars orbit each other with a time of 49.71 minutes (a light curve of the object and a real animation of the eclipse, just based on data from the Cassini telescope).
Gaia14aa is the third AM CVn known, but the first of its kind with a total eclipse. “So this is an extremely interesting fact, and we hope that others will follow thanks to Gaia,” concludes Altavilla.

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