The variability of the CoRoT target HD171834: gamma Dor pulsations and/or activity?
K. Uytterhoeven, P. Mathias, A. Baglin, M. Rainer, E. Poretti, P. Amado, E. Chapellier, L. Mantegazza, K. Pollard, J. C. Suarez, P. M. Kilmartin, K. H. Sato, R. A. Garcia, M. Auvergne, E. Michel, R. Samadi, C. Catala, F. Baudin
aa r X i v : . [ a s t r o - ph . S R ] N ov Astron. Nachr. / AN , No. 88, 789 – 792 (2010) /
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The variability of the CoRoT target HD171834: γ Dor pulsations and/oractivity? ⋆ K. Uytterhoeven ,⋆⋆ , P. Mathias , A. Baglin , M. Rainer , E. Poretti , P. Amado , E. Chapellier , L.Mantegazza , K. Pollard , J.C. Suarez , P.M. Kilmartin , K.H. Sato , R.A. Garc´ıa , M. Auvergne , E.Michel , R. Samadi , C. Catala , and F. Baudin Laboratoire AIM, CEA/DSM-CNRS-Universit´e Paris Diderot; CEA, IRFU, SAp, centre de Saclay, 91191, Gif-sur-Yvette, France Laboratoire d’Astrophysique de Toulouse-Tarbes, Universit´e de Toulouse, CNRS, 57 Avenue Azereix, 65000 Tarbes,France LESIA, UMR8109, Universit´e Pierre et Marie Curie, Universit´e Denis Diderot, Observatoire de Paris, 92195 Meudon,France INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy Instituto de Astrof´ısica de Andaluc´ıa (CSIC), Apartado 3004, 18080 Granada, Spain UMR 6525 H. Fizeau, UNS, CNRS, OCA, Campus Valrose, 06108 Nice Cedex 2, France Dep. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand Institut d’Astrophysique Spatiale, UMR 8617, Universit´e Paris XI, Bˆatiment 121, 91405 Orsay Cedex, FranceReceived 01 April 2010, accepted –Published online later
Key words stars: oscillations, stars: individual (HD171834), stars: variables: gamma Doradus starsWe present the preliminary results of a frequency and line-profile analysis of the CoRoT γ Dor candidate HD171834. Thedata consist of 149 days of CoRoT light curves and a ground-based dataset of more than 1400 high-resolution spectra,obtained with six different instruments. Low-amplitude frequencies between 0 and 5 d − , dominated by a frequency near0.96 d − and several of its harmonics, are detected. These findings suggest that HD171834 is not a mere γ Dor pulsatorand that stellar activity plays an important role in its variable behaviour. c (cid:13) It are exciting times for seismic studies of γ Dor pulsators,thanks to the successful operation of asteroseismic spacemissions, such as CoRoT (Baglin et al. 2006) and Kepler(Gilliland et al. 2010). The class of γ Dor stars (Kaye et al.1999) consists of stars of spectral types A-F that are slightlymore massive than the Sun (1.2Msun < M < ⋆ Based on observations made with ESO Telescopes at the La Silla Ob-servatory under the ESO Large Programmes ESO LP 178.D-0361 and ESOLP 182.D-0356, and on data collected at the Centro Astron´omico HispanoAlem´an (CAHA) at Calar Alto, operated jointly by the Max-Planck Insti-tut f¨ur Astronomie and the Instituto de Astrof´ısica de Andaluc´ıa (CSIC).Based on observations made with the Nordic Optical Telescope, operatedon the island of La Palma jointly by Denmark, Finland, Iceland, Norway,and Sweden, in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrof´ısica de Canarias. Also based on observations madeat Observatoire de Haute Provence (France) and at Mount John UniversityObservatory (New Zealand). The CoRoT space mission has been devel-oped and is operated by the French Space agency CNES in collaborationwith the Science Programs of ESA, ESA, Austria, Belgium, Brazil, Ger-many and Spain. ⋆⋆ e-mail: [email protected] et al. 2005; Grigahc`ene 2005). As only g-modes allow theprobing of the deep stellar interior, γ Dor stars are extremelyinteresting asteroseismic targets (e.g. Miglio et al. 2008).The γ Dor pulsators are however very challenging tar-gets, both from an observational as theoretical point of view.Their pulsation periods are of order of a day and hencevery difficult to monitor from the ground. Moreover, thecorresponding pulsation amplitudes are fairly small (below0.05mag and 2 km s − ). Several ground-based observationalefforts have been undertaken to describe the pulsational be-haviour in as many class members as possible (e.g. Poretti etal. 2002; Mathias et al. 2004; De Cat et al. 2006; Rodr´ıguezet al. 2006a,b; Uytterhoeven et al. 2008; Cuypers et al. 2009),resulting in the detection and identification of only a lim-ited amount of frequencies and associated mode parameters.Theoretically, the fast rotation observed in several γ Dorstars is posing problems in the description of the pulsationalinstability, as the current models do not account for higher-order rotational effects (Su´arez et al. 2005; Bouabid et al.2008, 2009; Moya et al. 2008).The CoRoT satellite disclosed for the first time the veryrich and complicated frequency spectrum, consisting of sev-eral hundreds of frequencies, of a γ Dor star (HD 49434,Chapellier et al. 2010). The first Kepler data of hundreds c (cid:13)
90 K. Uytterhoeven et al.: The variability of the CoRoT target HD171834
Fig. 1
Colour-magnitude diagram with the position ofHD171834 indicated (star). Dashed and solid tracks are evo-lutionary tracks for the overshooting extension distances 0.1and 0.2 (Claret 1995). The ZAMS, the borders of the δ Sct(black) and γ Dor (gray) instability strips are indicated byfull lines (Dupret et al. 2005).of γ Dor candidates reveal similar dense frequency spectra(Grigahc`ene et al. 2010), opening new prospectives in thestudy of the so far not-well understood class of γ Dor pul-sators. Moreover, the space data promise further investiga-tion of the nature of hybrid γ Dor- δ Sct pulsators, i.e. starsthat pulsate in g − and p − modes simultaneously, as severalhybrid candidates have been identified among the CoRoTand Kepler targets (Mathias et al. 2009; Grigahc`ene et al.2010). γ Dor candidate HD171834
The target of this paper is HD171834 (HIP91237; F3V; Vmag= 5.44). The star lies close to the red border of the γ Dor in-stability strip (see Fig.1), with effective temperature T eff =6750 ±
250 K, surface gravity log g = 3.9 ± ± γ Dorcandidate HD171834 appears to be photometrically con-stant from the ground (Poretti et al. 2003), but weak line-profile variations with low amplitudes have been reportedby Mathias et al. (2004).
The CoRoT satellite observed HD171834 for 149 days dur-ing its second Long Run in the center direction (LRc2, April-September 2008). To optimise the quality of the light curveswe corrected for time gaps caused by the passage of thesatellite through the South Atlantic Anomaly using the in-painting algorithm (Sato et al. 2010). The inpainted lightcurves were subsequently detrended and analysed in fre-quency with the Van´ıˇcek method (Van´ıˇcek 1971). The am-plitude periodogram shows no obvious peaks for frequen-cies higher than 15 d − (see Fig. 2). The highest ampli-tudes are reached for frequencies between 0 and 5 d − , with Fig. 2
Amplitude spectrum of the CoRoT data ofHD171834. The inset shows the frequency region 0-5d − in more detail.0.960 d − as dominant frequency. Harmonic frequencies seemto play an important role. In the framework of the ground-based follow-up observa-tions of CoRoT targets (Uytterhoeven et al. 2008a, 2009;Uytterhoeven 2009) HD171834 was monitored for two sea-sons (2008 and 2009) with six different instruments (see Ta-ble1) at the Observatory of Calar Alto (CaHa, Spain), Euro-pean Southern Observatory (ESO, Chile), Observatoire deHaute Provence (OHP, France), Mount John University Ob-servatory (MJUO, New Zealand), and Observatorio Roquede los Muchachos, La Palma (ORM, Spain). Never has therebeen a time-series with more than 1400 spectra for any other γ Dor star. The analysis was carried out on the Least-SquaresDeconvolved (LSD, Donati et al. 1997) spectra, calculatedwith mask T eff = 6750 K and log g =4.0, that were subse-quently normalised and corrected for instrumental radial ve-locity shifts (see Uytterhoeven et al. 2008 for a descriptionof the process). Figure 4 shows the radial velocities ( h v i )calculated from the LSD profiles. We did not find evidencefor a possibile binary nature of HD171834 in the spectra. The typical nightly line-profile variable behaviour of HD171834is illustrated in Fig. 3. Narrow, well-defined line-profile ‘ bumps ’are seen to propagate through the line-profile with periodslonger than a day. The individual datasets are too short to re-veal significant long-term variabilities. Therefore, we anal-ysed the combined datasets, spanning 414 days, and ex-cluded the more dispersed FOCES spectra as they intro-duced spurious frequencies (see bottom panel Fig. 4). Tosearch for periodicities in the time-series of LSD spectra weused the Van´ıˇcek method on the velocity moments (Aertset al. 1992), and performed a pixel-to-pixel analysis usingthe Intensity Period Search method (IPS, Telting & Schri-jvers 1997). In the variations of the first moment the CoRoTfrequency near 0.96 d − is recovered, together with sev- c (cid:13)2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim
Amplitude spectrum of the CoRoT data ofHD171834. The inset shows the frequency region 0-5d − in more detail.0.960 d − as dominant frequency. Harmonic frequencies seemto play an important role. In the framework of the ground-based follow-up observa-tions of CoRoT targets (Uytterhoeven et al. 2008a, 2009;Uytterhoeven 2009) HD171834 was monitored for two sea-sons (2008 and 2009) with six different instruments (see Ta-ble1) at the Observatory of Calar Alto (CaHa, Spain), Euro-pean Southern Observatory (ESO, Chile), Observatoire deHaute Provence (OHP, France), Mount John University Ob-servatory (MJUO, New Zealand), and Observatorio Roquede los Muchachos, La Palma (ORM, Spain). Never has therebeen a time-series with more than 1400 spectra for any other γ Dor star. The analysis was carried out on the Least-SquaresDeconvolved (LSD, Donati et al. 1997) spectra, calculatedwith mask T eff = 6750 K and log g =4.0, that were subse-quently normalised and corrected for instrumental radial ve-locity shifts (see Uytterhoeven et al. 2008 for a descriptionof the process). Figure 4 shows the radial velocities ( h v i )calculated from the LSD profiles. We did not find evidencefor a possibile binary nature of HD171834 in the spectra. The typical nightly line-profile variable behaviour of HD171834is illustrated in Fig. 3. Narrow, well-defined line-profile ‘ bumps ’are seen to propagate through the line-profile with periodslonger than a day. The individual datasets are too short to re-veal significant long-term variabilities. Therefore, we anal-ysed the combined datasets, spanning 414 days, and ex-cluded the more dispersed FOCES spectra as they intro-duced spurious frequencies (see bottom panel Fig. 4). Tosearch for periodicities in the time-series of LSD spectra weused the Van´ıˇcek method on the velocity moments (Aertset al. 1992), and performed a pixel-to-pixel analysis usingthe Intensity Period Search method (IPS, Telting & Schri-jvers 1997). In the variations of the first moment the CoRoTfrequency near 0.96 d − is recovered, together with sev- c (cid:13)2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim stron. Nachr. / AN (2010) 791 Table 1
Logbook of the observations of HD171834 in 2008 and 2009. The columns give information on the instrumentand observatory, the number of spectra (N), the timespan ( ∆ T, in days) of the dataset, the resolution of the spectrograph,and the observers.
Instrument Observatory N ∆ T ∆ T Resolution observer2008 [email protected] CaHa 562 25.2 34.1 40,000 [email protected] ESO 193 25.2 – 48,000 LM, [email protected] OHP 471 29.2 31.1 40,000 PM, [email protected] MJUO 55 9.1 – 35,000 KP, PMKFIES@NOT ORM 46 – 3.4 46,000 [email protected] ESO 79 – 39.1 80,000 EP, JCS
Fig. 3
Grayscale representation of one night of SOPHIEobservations (HJD 2454670) illustrating the typical nightlyline-profile variable behaviour of HD171834. Bottom: Av-erage LSD profile calculated from the SOPHIE time-seriesconsisting of 471 spectra. Top: Residual LSD profiles (HJD2454670) with respect to the average LSD profile.eral of its harmonics. The IPS method shows several low-amplitude frequencies between 0.1 and 1.0 d − , and har-monics of 0.96 d − . CoRoT data reveal that the γ Dor candidate HD171834 showslow-amplitude frequencies between 0 and 5 d − , dominatedby 0.96 d − and several of its harmonics, suggesting stellaractivity. The long-period low-amplitude variations are diffi-cult to detect from the ground. Only by combining all avail-able spectra, spanning more than one season and consistingof more than 1400 spectra are the frequencies recovered.A more detailed analysis is ongoing to confirm the doublenature of the variability, rotational and pulsational, and theirpossible connection and interplay. Also, spectropolarimetric Fig. 4
Radial velocities ( h v i ) calculated from the LSDprofiles of FEROS (black filled stars), SOPHIE (blue opencircles), FOCES (gray circles), HERCULES (blue filledcircles), HARPS (purple diamonds), and FIES (cyan openstars) spectra (top) obtained in 2008 and 2009. In the bot-tom panel we did not plot the more dispersed FOCES spec-tra, illustrating the low amplitude variability of HD171834.observations are scheduled with NARVAL@TBL to inves-tigate the possible importance of a magnetic field. Acknowledgements.
MR, EP, and LM acknowledge financial sup-port from the Italian ESS project, contract ASI/INAF I/015/07/0,WP 03170. EP acknowledges the support from the European He-lio and Asteroseismology Network (HELAS) for the participationto the Conference. This work has been partially funded by theGOLF/CNES grant at the CEA/Saclay.
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