|
RR Lyrae
campaign
|
|
Observation campain
of RR Lyr (spectroscopy + photometry) Call for observation from Jean-François Leborgne (IRAP, Observatoire Midi-Pyrénées, 14 Avenue Edouard Belin, F- TOULOUSE). About this star and the campaign, Jean-François says: Pulsations of RR Lyr stars (evolution status: horizontal branch; period ~0.5 days; V amplitude ~ 1 mag.) are still not well understood. Thought pulsating on similar modes as cepheids, they have smaller mass (~0.8Mo) and different internal structure: secondary phenomena not seen in cepheids are observed, such as period variations on years time scale and particularly the modulation of period and amplitude (Blazhko effect) on time scales of days to months. Blazhko effect is not observed on every RR Lyr stars and some, as RR Lyr itself, show variations of the Blazhko effect on years time scale. None of these phenomena has been satisfactorily explained by theory up to now. It is then important to characterize them by observations. One of the reason why such observations have not been intensively done yet is that they are very time consuming: a time resolution of minutes are necessary to study time scales from hours to years. It is then clear what contribution amateurs (equipped with modest size telescopes, CCD camera and possibly spectrograph) can bring to this research thanks to their availability and number. An intensive photometric campaign on the prototype star RR Lyr (mag. 7 to 8) is in progress since 4 years. It has shown a spectacular dimming of its Blazhko effect between 2008 and 2012.Though this phenomena is known since the 1960's no such intensive campaign has been done yet. In 2012, we reach a new step by including spectroscopic observations by amateurs. The aim is to study dynamical variations of chocs in stellar atmosphere and variations of stellar parameters (effective temperature, ...) as a function Blazhko effect status. RR Lyr is the only star on which such a research can be done because the other ones are much fainter having their magnitude at maximum at 9 at best. Two kinds of spectroscopic observations are implied in this research: low resolution spectrophotometry between 3500 and 7000A allowing the follow up hydrogen and metallic lines (especially CaII K line), observations at high resolution of Halpha line and some metallic lines which allow the follow up of the deformation of the line due to shock waves passing the atmosphere of the star during pulsation. Ephemeris of RR Lyr maximum prediction: http://rr-lyr.ast.obs-mip.fr/dokuwiki/doku.php?id=rrlyr2012 Contact: jean-francois.leborgne_at_irap.omp.eu Campagne d'observation de RR Lyr (spectrographie + photométrie) AD = 19 25 27.913, DEC = +42 47 03.69 (2000.0)
Une campagne d'observation photométrique intensive du prototype de ces étoiles, RR Lyr (mag. 7 à 8) est en cours depuis 4 ans. Elle a permis de mettre en évidence l'atténuation spectaculaire de son effet Blazhko entre 2008 et 2012. Quoique ce phénomène soit connu depuis les années 1960, aucune campagne d'observation aussi intense n'avait encore été effectuée. En 2012, un nouveau pas est franchi dans cette recherche en mettant à contribution des observations spectroscopiques par des amateurs. Il s'agit d'étudier les variations de la dynamique des chocs dans l'atmosphère et des paramètres stellaires (température effective, ...) en fonction de l'état de l'effet Blazhko. RR Lyr est la seule étoile sur laquelle ces observation sont possible car les autres étoiles de ce type sont beaucoup plus faibles, ayant leur maximum à la magnitude 9, au mieux. Deux types d'observations spectroscopiques sont impliquées dans cette recherche : des observations spectrophotométriques à basse résolution (R = 700 à 1000 typiquement) entre 3500 et 7000A permettant de suivre l'évolution des raies de l'hydrogène et de raies métalliques (en particulier la raie K de CaII), des observations à haute résolution (plus de R = 8000) de Halpha et de quelques raies métalique qui permettent de suivre les déformations des raies dues au passage d'ondes de choc dans l'atmosphère de l'étoile pendant la pulsation. Ephemeride des la prédiction des maximum de RR Lyr : http://rr-lyr.ast.obs-mip.fr/dokuwiki/doku.php?id=rrlyr2012 Contact: jean-francois.leborgne_at_irap.omp.eu |
Photometry
|
|
Spectrography During
the observation period the spectral type of RR Lyr change from F7
to A8 (in a very quisk time).
Detail of Halpha line Detection of choc wave Halpha line emission (around 22H28 UT - note the short duration of the event!)
H&K
lines observation during July 25, 2012 maximum
See here high resolution spectra of RR Lyr (eShel spectrograph at R = 10000) See also ARAS special topic about RR Lyr campaign |
