Merieme Chadid

Metal Abundances, Radial Velocities, and Other Physical Characteristics for the RR Lyrae Stars in The Kepler Field

Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude δ Sct star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which sixteen exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode. Spectroscopic [Fe/H] values for the 34 stars for which we were able to derive estimates range from –2.54 ± 0.13 (NR Lyr) to –0.05 ± 0.13 dex (V784 Cyg), and for the 19 Kepler-field non-Blazhko stars studied by Nemec et al. the abundances agree will with their photometric [Fe/H] values. Four non-Blazhko RR Lyrae stars that they identified as metal-rich (KIC 6100702, V2470 Cyg, V782 Cyg and V784 Cyg) are confirmed as such, and four additional stars (V839 Cyg, KIC 5520878, KIC 8832417, KIC 3868420) are also shown here to be metal-rich. Five of the non-Blazhko RRab stars are found to be more metal-rich than [Fe/H] ~–0.9 dex while all of the 16 Blazhko stars are more metal-poor than this value. New P-O_(31)^s-[Fe/H] relationships are derived based on ~970 days of quasi-continuous high-precision Q0-Q11 long- and short-cadence Kepler photometry. With the exception of some Blazhko stars, the spectroscopic and photometric [Fe/H] values are in good agreement. Several stars with unique photometric characteristics are identified, including a Blazhko variable with the smallest known amplitude and frequency modulations (V838 Cyg).

Atmospheric turbulence measurements at Ali Observatory, Tibet

The atmospheric turbulence characteristics are important to evaluate the quality of ground-based astronomical observatory. In order to characterize Ali observatory, Tibet. we have developed a single star Scidar (SSS) system, which is able to continuously monitor the vertical profiles of both optical turbulence and wind speed. The main SSS configuration includes a 40cm telescope and a CCD camera for fast sampling the star scintillation pattern. The SSS technique analyzes the scintillation patterns in real time, by computing the spatial auto-correlation and at least two cross-correlation images, and retrieves both C2 n (h) and V (h) vertical profiles from the ground up to 30km. This paper presents the first turbulence measurements with SSS at Ali observatory in October, 2011. We have successfully obtained the profiles of optical turbulence and wind speed, as well as the key parameters for adaptive optics, such as seeing, coherence time, and isoplanatic angle. The favourable results indicate that Ali observatory can be an excellent astronomical observatory.

The RRc Stars: Chemical Abundances and Envelope Kinematics

We analyzed series of spectra obtained for twelve stable RRc stars observed with the echelle spectro- graph of the du Pont telescope at Las Campanas Observatory and we analyzed the spectra of RRc Blazhko stars discussed by Govea et al. (2014). We derived model atmosphere parameters, [Fe/H] metallicities, and [X/Fe] abundance ratios for 12 species of 9 elements. We co-added all spectra ob- tained during the pulsation cycles to increase S/N and demonstrate that these spectra give results superior to those obtained by co-addition in small phase intervals. The RRc abundances are in good agreement with those derived for the RRab stars of Chadid et al. (2017). We used radial velocity measurements of metal lines and H{\alpha} to construct variations of velocity with phase, and center-of-mass velocities. We used these to construct radial-velocity templates for use in low-medium resolution radial velocity surveys of RRc stars. Additionally, we calculated primary accelerations, radius variations, metal and H{\alpha} velocity amplitudes, which we display as regressions against primary acceleration. We employ these results to compare the atmosphere structures of metal-poor RRc stars with their RRab counterparts. Finally, we use the radial velocity data for our Blazhko stars and the Blazhko periods of Szczygie l & Fabrycky (2007) to falsify the Blazhko oblique rotator hypothesis.

Opening a new window on the southern stars for less money: PAIX the first Antarctica polar mission photometer

In this invited paper, we implement a new way to study the stellar oscillations, pulsations and their evolutionary properties with long uninterrupted and continuous precision observations over 150 days from the ground, and without the regular interruptions imposed by the earth rotation. PAIX–First Robotic Antarctica Polar Mission– gives a new insight to cope with unresolved stellar enigma and stellar oscillation challenges and offers a great opportunity to benefit from an access to the best astronomical site on Earth –DomeC–. The project is made of low cost commercial components, and achieves astrophysical measurement time-series of stellar physics fields, challenging photometry from space that shows large gaps in terms of flexibility during the observing runs, the choice of targets, the repair of failures and the inexorable high costs. PAIX has yet more advantages than space missions in observing in UBV RI bands and then collecting unprecedented simultaneous multicolor light curves of several targets. We give a brief history of the Astronomy in Antarctica and describe the first polar robotized mission PAIX and the outcome of stellar physics from the heart of Antarctica during several polar nights. We briefly discuss our first results and perspectives on the pulsating stars and its evolution from Antarctica, especially the connection between temporal hydrodynamic phenomena and cyclic modulations. Finally, we highlight the impact of PAIX on the stellar physics study and the remaining challenges to successfully accomplish the Universe explorations under extreme conditions.

Window to the universe for less money: 10 years of PAIX in Antarctica

Time has come to implement a new way to study the stellar physics from the ground with long-term uninterrupted time series, multi-color photometry, flexibility during observing runs and all for less money. PAIX, Photometer AntarctIca eXtinction, gives new insight to cope with unresolved stellar enigma and stellar oscillation challenges and bears witness, for the first time, to a new technology of the polar instrumental robotization under extreme human and weather conditions in the heart of Antarctica. In fact, the stellar pulsation plays a crucial role in understanding the Universe, however progress is limited by the data accuracy needed to detect numerous modes of oscillations with small amplitudes and by the discontinuous nature of typical ground-based data strings which often introduce ambiguities in the determination of oscillation frequencies. The recent space missions enable to overcome both difficulties, However, the outcome of the space missions shows large gaps in terms of flexibility during the observing runs, the choice of targets, the repair of failures and the inexorable high costs. We present here the new technology from Antarctica, in particular from South Polar Site Dome C that benefits from great image quality and 150 days high time coverage, where the seeing reaches a median value of 1 arcsec during the polar night. We briefly describe the instrumental performances of PAIX, its low-cost commercial components, robotic telescope, multi-band photometer and automatic control, working under harsh weather conditions, even when the temperature reach values as low as -80°C. The polar mission PAIX challenges the space missions and even has more advantages than CoRoT and KEPLER in observing in UBVRI bands and then collecting multicolor light curves simultaneously of several targets. We discuss here the first outcomes of stellar physics from the heart of Antarctica during 10 polar nights and PAIX new results and perspectives on the pulsating stars from Antarctica, especially the connection between the stellar pulsation enigma and the Universe mysteries. Finally, we highlight the impact of PAIX -the robotic Antarctica photometer- on the Astronomy development.

SCIDAR: an optical turbulence profiler for Dome A

This paper introduces a plan to detect turbulence profiles at Dome A with a Single Star Scidar (SSS), to enhance our understanding of the characteristics of the site. The development of a portable monitor for profiling vertical atmospheric optical turbulence and wind speed is presented. By analyzing the spatial auto and cross-correlation functions of very short exposure images of single star scintillation patterns, the SSS can provide the vertical profiles of turbulence intensity C n (h) and wind speed V (h). A SSS prototype is already operational at Ali in Tibet which will be improved in order to become fully robotic and adapted to extreme weather conditions that prevail at Dome A in Antarctica.