Weather in Bologna

August 21, 2018, 3:55 am
real feel: 21°C
current pressure: 1020 mb
humidity: 73%
wind speed: 3 m/s SSW
sunrise: 6:24 am
sunset: 8:11 pm

RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia

Left panels: 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.

During the first part of the Gaia mission in Ecliptic Pole Scanning Law, Gaia frequently observed the South Ecliptic Pole (SEP) which covers an external region of the Large Magellanic Cloud (LMC). A couple of hundred RR Lyrae stars are known to populate the central 1 square degree of the Gaia SEP. Their typical average apparent magnitudes are around 19.5 mag in V. The magnitude of RR Lyrae stars is fainter and amplitudes are larger in blue photometric bands.

The figure  shows in the left panels, the G-band light curves of three fundamental-mode RR Lyrae (RRab) stars in the Gaia SEP field in the LMC. They consist of 118, 74 and 96 observations spread over a total time elapse of 28 days. Observations with estimated uncertainties larger than 0.05 mag were excluded from all plots. Median uncertainties of the measurements are around 0.02 mag.

Gaia light curves have been folded using periods taken from the OGLE IV catalogue of variable stars in the Gaia SEP (Soszynski et al. 2012, AcA, 62, 219). OGLE I-band light curves for these stars are shown in the right panels for comparison. The effective wavelengths of OGLE I-band and Gaia G-band are different (the latter being shorter wavelengths). Because of this difference in the photometric bands, the magnitudes are fainter and the amplitudes are larger in the G-band.

Gaia’s photometry, even at the faint magnitudes of the LMC RR Lyrae stars and after a first data reduction, allows us to clearly see features such as the “bump” just before minimum light and the “hump” before maximum light, typical for RRab light curves. These features will become even better defined when the data will be further calibrated and when the standard deviations decrease.

See also the Gaia image of the week

Credits: ESA/Gaia/DPAC/CU5/CU7/INAF-OABo, Gisella Clementini, Dafydd Evans, Laurent Eyer, Krzysztof Nienartowicz, Lorenzo Rimoldini and the Geneva CU7/DPCG and CU7/INAF-OACN teams.