* Astronomy

Members Login
Post Info TOPIC: RR Lyrae stars


L

Posts: 131433
Date:
RE: RR Lyrae stars
Permalink  
 


Title: Non-Blazhko RR Lyrae Stars Observed with the KEPLER Space Telescope
Authors: J.M. Nemec (1,2), R. Smolec (3), J.M. Benko (4), P. Moskalik (5), K. Kolenberg (3,6), R. Szabo (4), D.W. Kurtz (7), S. Bryson (8), E. Guggenberger (3), M. Chadid (9), Y.-B. Jeon (10), A. Kunder (12), A.C. Layden (13), K. Kinemuchi (8), L.L. Kiss (4), E. Poretti (14), J. Christensen-Dalsgaard (11), H. Kjeldsen (11), D. Caldwell (15), V. Ripepi (16), A. Derekas (4), J. Nuspl (4), F.Mullally (15), S.E. Thompson (15), W.J. Borucki (8) ((1) Department of Physics and Astronomy, Camosun College, Victoria, Canada (2) International Statistics and Research Corporation, Brentwood Bay, Canada (3) Institut fur Astronomie, University of Vienna, Vienna, Austria (4) Konkoly Obs.Hung.Acad.Sciences, Budapest, Hungary (5) Copernicus Astronomical Center, Warsaw, Poland (6) Harvard College Observatory, Cambridge, USA (7) Jeremiah Horrocks Institute of Astrophysics, Univ. Central Lancashire, UK (8) NASA Ames Research Center, Moffett Field, CA, USA (9) Obs. Cote d'Azur, Univ.Nice Sophia-Antipolis, Parc Valrose, France (10) Korea Astronomy and Space Science Institute, Daejeon, Korea (11) Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark (12) Cerro Tololo Inter-American Observatory, La Serena, Chile (13) Physics and Astronomy Dept., Bowling Green State University, OH, USA (14) Osservatorio Astronomico di Brera, Merate, Italy (15) SETI Institute/NASA Ames Research Centre, Moffett Field, CA, USA (16) INAF-Osservatorio Astronomico di Capodimonte, Napoli, Italy)

This paper summarises the main results of our recent study of the non-Blazhko RR Lyrae stars observed with the Kepler space telescope. These stars offer the opportunity for studying the stability of the pulsations of RR Lyrae stars and for providing a reference against which the Blazhko RR Lyrae stars can be compared. Of particular interest is the stability of the low-dispersion (sigma < 1mmag) light curves constructed from ~18,000 long-cadence (30-min) and (for FN Lyr and AW Dra) the ~150,000 short-cadence (1-min) photometric data points. Fourier-based [Fe/H] values and other physical characteristics are also derived. When the observed periods are compared with periods computed with the Warsaw non-linear convective pulsation code better agreement is achieved assuming pulsational L and M values rather than the (higher) evolutionary L and M values.

Read more  (3365kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: RR Lyrae the Stellar Beacons of the Galactic Structure
Authors: Giuseppe Bono (1,2), Massimo Dall'Ora (3), Filippina Caputo (2), Giuseppina Coppola (3), Katia Giovenali (1), Marcella Marconi (3), Anna Marina Piersimoni (4), Robert F. Stellingwerf (5) ((1) Universit'a di Roma Tor Vergata, Roma, Italy, (2) INAF-Osservatorio Astronomico di Roma, Italy, (3) INAF-Oservatorio Astronomico di Capodimonte, Napoli, Italy, (4) INAF-Oservatorio Astronomico di Collurania, Teramo, Italy, (5) Stellingwerf Consulting, AL, USA)

We present some recent findings concerning the use of RR Lyrae as distance indicators and stellar tracers. We outline pros and cons of field and cluster RR Lyrae stars and discuss recent theoretical findings concerning the use of the Bailey (amplitude vs pulsation period) diagram to constrain the possible occurrence of Helium enhanced RR Lyrae stars. Nonlinear, convective RR Lyrae models indicate that the pulsation properties of RR Lyrae stars are minimally affected by the helium content. The main difference between canonical and He enhanced models is due to the increase in luminosity predicted by evolutionary models. Moreover, we focus our attention on the near-infrared Period-Luminosity (PL) relation of RR Lyrae and summarize observational evidence concerning the slope of the K-band PL relation in a few globulars (M92, Reticulum, M5, Omega Cen) covering a range in metallicity of ~1 dex. Current findings suggest that the slope has a mild dependence on the metal content when moving from the metal-poor to the metal-intermediate regime.
Finally, we also discuss the use of RR Lyrae stars either to estimate (helium indicator: A-parameter) or to measure (absorption and emission lines) the helium content.

Read more (53kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: RR Lyrae Research with the Kepler Mission
Authors: K. Kinemuchi

The Kepler Mission is a Discovery mission supported by NASA's Science Mission Directorate, and its primary aim is to discover Earth-sized planets in the habitable zone of solar-type stars. The space telescope was designed with a photometer that monitors the Kepler field in a near continuous manner in order to achieve this goal. With this mission, the asteroseismology community also benefits from the Kepler data via the abundant time-series photometry. With a short cadence of 1 minute and long cadence of 30 minute observations, the time coverage for many variable stars is unprecedentedly complete. The Kepler field also contains the archetype RR Lyr, and the Kepler Asteroseismic Science Consortium (KASC) Working Group for RR Lyrae stars have been working to uncover the mysteries surrounding these stars. I will provide an overview of the Kepler program in relation to RR Lyrae research.

Read more (1028kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: CoRoT light curves of RR Lyrae stars. CoRoT 101128793: long-term changes in the Blazhko effect and excitation of additional modes
Authors: Ennio Poretti, Margit Paparo, Magali Deleuil, Merieme Chadid, Katrien Kolenberg, Robert Szabo, Jozsef M. Benko, Eric Chapellier, Elisabeth Guggenberger, Jean-Francois Le Borgne, Florent Rostagni, Herve Trinquet, Michel Auvergne, Annie Baglin, Luis M. Sarro, Werner W. Weiss

The CoRoT (Convection, Rotation and planetary Transits) space mission provides a valuable opportunity to monitor stars with uninterrupted time sampling for up to 150 days at a time. The study of RR Lyrae stars, performed in the framework of the Additional Programmes belonging to the exoplanetary field, will particularly benefit from such dense, long-duration monitoring. The Blazhko effect in RR Lyrae stars is a long-standing, unsolved problem of stellar astrophysics. We used the CoRoT data of the new RR Lyrae variable CoRoT 101128793 (f0=2.119 c/d, P=0.4719296 d) to provide us with more detailed observational facts to understand the physical process behind the phenomenon. The CoRoT data were corrected for one jump and the long-term drift. We applied different period-finding techniques to the corrected timeseries to investigate amplitude and phase modulation. We detected 79 frequencies in the light curve of CoRoT 101128793. They have been identified as the main frequency f0, and its harmonics, two independent terms, the terms related to the Blazhko frequency, and several combination terms. A Blazhko frequency fB=0.056 c/d and a triplet structure around the fundamental radial mode and harmonics were detected, as well as a long-term variability of the Blazhko modulation. Indeed, the amplitude of the main oscillation is decreasing along the CoRoT survey. The Blazhko modulation is one of the smallest observed in RR Lyrae stars. Moreover, the additional modes f1=3.630 and f2=3.159 c/d are detected. Taking its ratio with the fundamental radial mode into account, the term f1 could be the identified as the second radial overtone. Detecting of these modes in horizontal branch stars is a new result obtained by CoRoT.

Read more (517kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: First Kepler results on RR Lyrae stars
Authors: K. Kolenberg, R. Szabó, D. W. Kurtz, R. L. Gilliland, J. Christensen-Dalsgaard, H. Kjeldsen, T. M. Brown, J. M. Benkö, M. Chadid, A. Derekas, M. Di Criscienzo, E. Guggenberger, K. Kinemuchi, A. Kunder, Z. Kolláth, G. Kopacki, P. Moskalik, J. M. Nemec, J. Nuspl, R. Silvotti, M. D. Suran, W. J. Borucki, D. Koch, J. M. Jenkins

We present the first results of our analyses of selected RR Lyrae stars for which data have been obtained by the Kepler Mission. As expected, we find a significant fraction of the RRab stars to show the Blazhko effect, a still unexplained phenomenon that manifests itself as periodic amplitude and phase modulations of the light curve, on time scales of typically tens to hundreds of days. The long time span of the Kepler Mission of 3.5 yrs, and the unprecedentedly high precision of its data provide a unique opportunity for the study of RR Lyrae stars.
Using data of a modulated star observed in the first roll as a showcase, we discuss the data, our analyses, findings, and their implications for our understanding of RR Lyrae stars and the Blazhko effect. With at least 40% of the RR Lyrae stars in our sample showing modulation, we confirm the high incidence rate that was only found in recent high-precision studies. Moreover, we report the occurrence of additional frequencies, beyond the main pulsation mode and its modulation components. Their half-integer ratio to the main frequency is reminiscent of a period doubling effect caused by resonances, observed for the first time in RR Lyrae stars.

Read more (572kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: RR Lyrae Pulsation Theory
Authors: Marcella Marconi

RR Lyrae stars play an important role as distance indicators and stellar population tracers. In this context the construction of accurate pulsation models is crucial to understand the observed properties and to constrain the intrinsic stellar parameters of these pulsators. The physical mechanism driving pulsation in RR Lyrae stars has been known since the middle of the 20th century and many efforts have been performed during the last few decades in the construction of more and more refined pulsation models. In particular, nonlinear pulsation models including a nonlocal time-dependent treatment of convection, such as the ones originally developed in Los Alamos in the seventies, allow us to reproduce all the relevant observables of radial pulsation and to establish accurate relations and methods to constrain the intrinsic stellar properties and the distance of these variables. The most recent results on RR Lyrae pulsation obtained through these kinds of models will be presented and a few still debated problems will be discussed.

Read more (582kb, PDF)

__________________


L

Posts: 131433
Date:
RR Lyraes
Permalink  
 


Title: Substructure revealed by RR Lyraes in SDSS Stripe 82
Authors: L.L. Watkins (1), N.W. Evans (1), V. Belokurov (1), M.C. Smith (1), P.C. Hewett (1), D.M. Bramich (2), G.F. Gilmore (1), M.J. Irwin (1), S. Vidrih (3,4), L. Wyrzykowski (1), D. Zucker (5) ((1) Cambridge, (2) ING, (3) Heidelberg, (4) Ljubljana, (5) Macquarrie)

We present an analysis of the substructure revealed by 407 RR Lyraes in Sloan Digital Sky Survey (SDSS) Stripe 82. Period estimates are determined to high accuracy using a string-length method. A subset of 178 RR Lyraes with spectrally derived metallicities are employed to derive metallicity-period-amplitude relations, which are then used to find metallicities and distances for the entire sample. The RR Lyraes lie between 5 and 115 kpc from the Galactic center. They are divided into subsets of 316 RRab types and 91 RRc types based on their period, colour and metallicity. The density distribution is not smooth, but dominated by clumps and substructure. Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the Hercules-Aquila Cloud respectively are identified. Hence, ~ 70 % of the RR Lyraes in Stripe 82 belong to known substructure. There is a sharp break in the density distribution at Galactocentric radii of 40 kpc, reflecting the fact that the dominant substructure in Stripe 82 - the Hercules-Aquila Cloud and the Sagittarius Stream - lies within 40 kpc. In fact, almost 60 % of all the RR Lyraes in Stripe 82 are associated with the Hercules-Aquila Cloud alone, which emphasises its pre-eminence. Additionally, evidence of a new and distant substructure - the Pisces Overdensity - is found, consisting of 28 faint RR Lyraes centred on Galactic coordinates (80 deg, -55 deg) and with distances of ~ 80 kpc. The total stellar mass in the Pisces Overdensity is ~10000 solar masses and its metallicity is [Fe/H] ~ -1.5.

Read more  (1064kb, PDF)

__________________


L

Posts: 131433
Date:
RR Lyrae stars
Permalink  
 


Title: Carbon-rich RR Lyr type stars
Authors: George Wallerstein, V. V. Kovtyukh, S. M. Andrievsky

We have derived CNO abundances in 12 RR Lyrae stars. Four stars show [C/Fe] near 0.0 and two stars show [C/Fe] = 0.52 and 0.65. Red giant branch stars, which are known to be the predecessors of RR Lyrae stars, generally show a deficiency of carbon due to proton captures during their evolution from the main sequence up the giant branch. We suggest that the enhancement of carbon is due to production during the helium flash combined with mixing to the surface by vigorous convection induced by the flash itself.

Read more (19kb, PDF)

__________________
«First  <  1 2 | Page of 2  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard