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Multi-site, multi-technique survey of γ Doradus candidates. I. Spectroscopic results for 59 stars
We present the first results of a 2-year high-resolution spectroscopycampaign of 59 candidate γ Doradus stars which were mainlydiscovered from the HIPPARCOS astrometric mission. More than 60% of thestars present line profile variations which can be interpreted as due topulsation related to γ Doradus stars. For all stars we alsoderived the projected rotation velocity (up to more than 200 kms-1). The amplitude ratios 2K/Δ m for the mainHIPPARCOS frequency are in the range 35-96 kms-1,mag-1. About 50% of the candidates arepossible members of binary systems, with 20 stars being confirmedγ Doradus. At least 6 stars present composite spectra, and in allbut one case (for which only one spectrum could be obtained), the narrowcomponent shows line profile variations, pointing towards anuncomfortable situation if this narrow component originates from a shellsurrounding the star. This paper is the first of a series concerningmode identification using both photometric and spectroscopic methods forthe confirmed γ Doradus stars of the present sample.Partially based on observations obtained at the Observatoire deHaute-Provence.
| A Dozen New γ Doradus Stars
We use new high-dispersion spectroscopic and precise photometricobservations to identify 12 new γ Doradus stars. Two of the 12systems are double-lined binaries that show obvious velocityvariability. Five other stars have metallic lines with compositeprofiles characterized by a narrow feature near the center of each broadcomponent. Spectrograms of the Hα line indicate that all fivestars are binaries rather than shell stars. The remaining five stars inour sample are probably single. All 12 stars are photometricallyvariable with amplitudes between 6 and 87 mmag in Johnson B and periodsbetween 0.3 and 1.2 days. Four stars are monoperiodic; the rest havebetween two and five independent periods. The variability at all periodsapproximates a sinusoid. Although many of the stars lie within theδ Scuti instability strip, none exhibit the higher frequencyvariability seen in δ Scuti stars. We have increased the sample ofknown γ Doradus stars by 40% and revised the positions of a numberof variables in the H-R diagram by accounting for duplicity. Our list of42 confirmed γ Doradus variables gives some of their properties.All are dwarfs or subgiants and lie within a well-defined region of theH-R diagram that overlaps the cool edge of the δ Scuti instabilitystrip. We compare the observed location of the γ Doradus variableswith a recently published theoretical γ Doradus instability stripand find good agreement.
| A Theoretical γ Doradus Instability Strip
In this paper, we present the first theoretical γ Doradusinstability strip. We find that our model instability strip agrees verywell with the previously established, observationally based, instabilitystrip of Handler & Shobbrook. We stress, as do Guzik et al., thatthe convection zone depth plays the major role in the determination ofour instability strip. Once this depth becomes too deep or too shallow,the convection zone no longer allows for pulsational instability. Ourtheoretical γ Dor instability strip is bounded by ~6850 and 7360 Kat the red and blue edge, respectively, on the zero-age main sequenceand by ~6560 and 7000 K at the red and blue edge, respectively,approximately 2 mag more luminous. This theoretical strip, transformedto the observer's color-magnitude diagram, overlays the region wheremost of the 30 bona fide γ Dor stars are found.
| Six New γ Doradus Stars
We present high-resolution spectroscopy and precision photometry of sixnew γ Doradus stars, one of which was independently discovered byanother group. This brings the total number of confirmed γ Doradusvariables to 30. All six of these variables fall in the spectral classrange F0-F2 all but one are subgiants. The six stars have between oneand five photometric periods in the range 0.3-1.2 days. We find noevidence for higher frequency δ Scuti pulsations in any of thesesix stars. Our spectroscopic observations reveal HD 108100 to be thefirst confirmed γ Doradus variable with composite broad and narrowline profiles suggesting the presence of a circumstellar shell or disk.HD 221866 has the most asymmetric absorption lines of the six stars inthis paper and also the largest photometric amplitude. Most of the 30confirmed γ Doradus variables lie in a fairly tight region of theH-R diagram on or just above the main sequence that partially overlapsthe cool edge of the δ Scuti instability strip. However, threestars, including two of the new variables in this paper, are subgiantsthat lie well within the δ Scuti strip. Among the 30 confirmedγ Doradus variables, we find no correlation between thephotometric periods and intrinsic color, absolute magnitude, orluminosity.
| The multiperiodicity of the gamma Doradus stars HD 224945 and HD 224638 as detected from a multisite campaign
We discuss new photometric data collected on the gamma Dor variables HD224945 and HD 224638. Multiperiodicity was detected in both stars,thanks to the clear spectral window of a multisite campaign thatinvolved five observatories. HD 224945 shows the shortest period amongthe gamma Dor stars, i.e., 0.3330 d. The pulsation behaviour is verydifferent: HD 224945 displays a set of frequencies spread over aninterval much larger than that of HD 224638. We clearly found evidencefor amplitude variations in the excited modes by comparing data fromdifferent years. HD 224945 and HD 224638 are among the best examples ofgamma Dor stars that show multimode pulsations, which make them veryinteresting from an asteroseismological point of view. Based onobservations partially collected at ESO-La Silla (Proposals 54.E-018 and56.E-0308).
| Search for gamma Doradus variable stars in the Pleiades cluster
Photometric observations in the uvbybeta system of A-F type stars in thePleiades cluster have been performed in order to detect pulsatingvariable stars of gamma Doradus type in the lower part of the Cepheidinstability strip. In order to obtain more information about thebehaviour of the studied objects and to be able to distinguish betweenlong period variable and non-variable stars, two statistical methodshave been developed. Several of these stars show some type ofvariability but only two of the observed objects, H1284 and S29, can besafely classified as gamma Dor stars. Furthermore, these observationshave provided us with Strömgren and Hβ photometry,non-existing up to now for some of them, which permitted us to perform aphotometric study of the Pleiades cluster.
| Gamma Doradus Stars: Defining a New Class of Pulsating Variables
In this paper we describe a new class of pulsating stars, the prototypeof which is the bright, early, F-type dwarf gamma Doradus. These starstypically have between 1 and 5 periods ranging from 0.4 to 3 days withphotometric amplitudes up to 0.1 mag in Johnson V. The mechanism forthese observed variations is high-order, low-degree, nonradial,gravity-mode pulsation.
| The gamma DOR variable HR 8799: results from a multisite campaign
In this paper, we present the results of a multisite photometriccampaign devoted to the gamma Doradus type variable HR 8799. FromJohnson and Stromgren data, we were able to identify three independentfrequencies (f_1= 1.9791 cycle d^-1, f_2=1.7268 cycle d^-1 andf_3=1.6498 cycle d^-1) as well as another signal, which we are able toidentify as the coupling term between two of the frequencies(f_4=f_1-f_2=0.2479 cycle d^-1). These four frequencies are able toaccount for all of the observed variations down to the 1sigmasignificance level. We discuss another possible interpretation of thesefrequencies using a model of quasi-stochastic amplitude modulation. Inthis scenario, we are able to show that HR 8799 might be pulsating withtwo independent frequencies, one of which undergoes amplitude modulationsimilar to other gamma Dor objects. In addition, we discuss apreliminary mode identification based on the observed colour curves.Finally, 18 simultaneous, high-resolution echelle spectra were collectedon two nights and we qualitatively compare the radial velocities fromthese data with our photometry.
| Discovery and analysis of Gamma Doradus type pulsations in the F0 IV star HR 2740=QW PUP
We present multisite photometric observations of the F0 IV star HR2740=QW Pup that reveal it to be a Gamma Dor type variable pulsatingwith four frequencies: 1.0434, 0.9951, 1.1088 and 0.9019/d. These datawere obtained over a time baseline spanning from January 14 to February11, 1997. The 1.0434/d term dominates in amplitude (10 mmag) over theother three (each less than 5 mmag); the light curve comprising thesefour frequencies seems to be very stable and no residual power is leftin the power spectrum. During the analysis particular attention was paidto methodological aspects, which cannot be neglected considering theproximity of the frequencies to 1/d. Physical parameters were alsoderived for all the well-known Gamma Dor stars, confirming that thisclass is very homogenous. In the framework of the campaign, two Ap starswere also observed. The photometric differences between these rotatingvariables and HR 2740 are emphasized, corroborating the pulsationalnature of the Gamma Dor stars. It is further demonstrated that therotational splitting cannot be a suitable explanation of the observedfrequency content of HR 2740.
| The Gamma DOR variable HD 164615 - Results from a multisite photometric campaign
We present the results from a multisite photometric campaign devoted tothe Gamma Dor variable HD 164615. During the campaign, data werecollected in the Johnson and Stromgren photometric systems. A firstsearch for sinusoidal periodicities yielded a three-term solution withfrequencies f1 = 1.2328, f2 = 1.0899, and f3 = 2.3501/d, and a long-termtrend f4 = 0.1301/d. The star may therefore be multiperiodic with eachfrequency related to a pulsation mode. However, a further examination ofthe curve provided evidence that the amplitude at the instant of maximumbrightness is modulated. Alternatively, HD 164615 may be a monoperiodicvariable with frequency f1 = 1.2321/d, showing amplitude modulation withfrequency f4 = 0.1301/d. The presence in the power spectra of thecoupling terms f2 = f1 - f4 and f3 = f1 + f4 - 1 supports the latterinterpretation. In the monoperiodic case the previously giveninterpretation based on a spot carried through the visible disk byrotation still holds, provided that the spot is bright and evolves on atime scale of a few days. However, similarities with other Gamma Dorstars provide indirect indication in favor of the existence of anonradial pulsation interpretation.
| The gamma Doradus-type variable 9 Aurigae: results from a multi-site campaign
We present the results of a multi-longitude coordinated photometriccampaign on the gamma Dor variable 9 Aur. Three frequencies can bedetermined from the data (f_1=0.7948, f_3=0.7679, f_5=0.3429 d^-1) twoof them have already been recognized in past seasons while the thirdfrequency is reported for the first time. Analysis shows that the thirdwas `turned off' or present with an amplitude below the limits ofdetection during previous observing seasons. This evidence, togetherwith consistent amplitude changes in the two previously recognizedsignals, suggests that the stellar structure responsible for 9 Aur'svariability is extremely dynamic. Intermediate-resolution spectra andCORAVEL radial velocities collected simultaneously show variability ontime-scales commensurable with the photometry. The only sensibleexplanation appears to be a non-radial pulsation (NRP) model. However,results obtained reveal a number of features that deviate from classicalNRP behaviour. Such features are emphasized in this paper in support ofthe future development of a specific NRP model - a model which has yetto be elucidated for gamma Dor-type variables.
| The 73rd Name-List of Variable Stars
Not Available
| Mode identification of the slowly pulsating F0V star V398 Aurigae (9 Aur).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.278..877A&db_key=AST
| A Search for Gamma-Doradus Type Variable Stars in the Hyades
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995MNRAS.277.1404K&db_key=AST
| Multi-longitude campaigns on gamma Doradus stars
gamma Doradus stars constitute a new class of variables (Krisciunas1995). They have spectral types near F0 V and are variable up to 0.10mag in V on time scales of 0.5 to 3 days. Krisciunas & Handler(1995) list 17 bona fide examples and candidates. The mechanism forvariability appears to be non-radial gravity mode pulsations. Thisconclusion derives from the time scale of the variability (an order ofmagnitude longer than the fundamental radial pulsation period for starsof this density), radial velocity and spectral line profile variationsthat correlate with the photometric variations (Krisciunas et al. 1995;Balona et al. 199[6]), and lack of evidence for other explanations.Starspots are proposed by some (e.g. Zerbi 199[6]) as an alternativeexplanation to non-radial g-modes, but with at least 3 periods for twoof the stars and lack of evidence for chromospheric activity, we do notsee how the starspot idea is viable. Recently Aerts & Krisciunas(199[6]) and Balona et al. (199[6]) have identified the pulsation modesof two stars, V398 Aur (= 9 Aur) and gamma Doradus itself. In thisposter we present results of multi-longitude campaigns carried out fromNovember 1994 through October 1995 on gamma Dor, V398 Aur, HD 164615, BS8799, HD 224638, and HD 224945. Multi-longitude campaigns are necessaryfor the proper identification of the frequencies of variation, owing toaliasing that results from observations, at a single site, of stars withperiods on the order of one day. Aerts C., Krisciunas K., 199[6], MNRAS,in press Balona L. A. et al. 199[6], MUSICOS conference proceedings, inpress Krisciunas K., 1995, ``What is known and not known about gammaDoradus stars,'' Delta Scuti Star Newsletter, Issue 9, 17 Krisciunas K.et al. \ 1995, MNRAS, 273, 662 Krisciunas K., Handler G., 1995, IBVS4195 Zerbi F. M., 199[6], Vienna meeting on Stellar Surface Structure,IAU Symposium 176, in press
| The complex photometric behaviour of the δ Scuti star HD 224639.
HD 224639 was photometrically observed for 20h in 1989 and 120h in 1991(454 and 2567 datapoints, respectively). The star shows a very complexpulsational content with 3 components with semi-amplitudes of about15mmag and many other terms with a smaller semi-amplitude. The 1991dataset allowed us to single out 11 components in the frequency rangebetween 5 and 12 c/d, but many more are probably present since theresidual rms of the fit is 8.6mmag, while the noise level is expected tobe 3.7mmag. By subdividing the 1991 dataset into two parts and bycomparing the results of the frequency analysis with those obtained fromthe 1989 dataset we found independent evidence in support of thereliability of four frequencies: 6.21, 8.49, 9.54 and 11.42 c/d. Sincemost of the 11 components are nonradial modes, their identification ishampered by the high rotational velocity (vsin i=110km/s) which veryprobably produces the splitting of an l mode into a multiplet(-l<=m<=+l) and, in any case, causes an appreciable shift infrequency of the central value (m=0).
| Young Pulsating Stars in the Bohm-Vitense Decrement
Not Available
| 9 Aurigae: strong evidence for non-radial pulsations
We present further photometric observations of the unusual F0 V star 9Aurigae and present evidence that this star's radial velocity,spectroscopic line widths and line depths are also variable with thesame frequencies as the photometric data (f_1~=0.795 and f_2~=0.345d^-1). The phases of these sinusoids are stable over time-scales oflonger than one year, though the amplitudes can vary, making theprediction of photometric behaviour impossible. Given that a variety ofother explanations have already been discounted (e.g. interactions witha close companion, the existence of a lumpy, orbiting ring of dust, orstar spots) and that these variations occur on time-scales an order ofmagnitude slower than the fundamental radial pulsation period, we havevery strong evidence that 9 Aurigae exhibits non-radial g-modepulsations. Since the power spectrum of the radial velocity data showsfrequency f_2 but does not clearly show f_1, the present data suggestthat f_2 is associated with a low-degree spherical harmonic L=1 or 2),while f_1 is associated with a higher degree harmonic. 9 Aurigae, alongwith such stars as gamma Doradus, HD 224638, HD 224945, and HD 164615,appears to constitute a new class of pulsating variables. These starsare to be found at or beyond the cool edge of the Cepheid instabilitystrip in the HR Diagram. Prior to this, only much hotter stars have beenshown to exhibit non-radial g-modes.
| A long period early F-type variable: HR8799
Not Available
| Gamma-Doradus - Evidence for a New Class of Pulsating Star
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.270..905B&db_key=AST
| Unusual Variability among Early F-Type Stars - HD224638 and HD224945
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.270..439M&db_key=AST
| Unusual Photospheric Activity in Stars of Spectral Type FO-F5
Not Available
| The sign of four : a new class of cool non-radially pulsating stars ?
In this paper we discuss four early F-type variable stars whose periodsare an order of magnitude slower than known pulsators of comparableluminosity. They cannot be stars undergoing simple radial pulsations.For one or more of these stars we can discount the possibility that thevariability is due to rotational modulation of star spots, interactionswith (or tidal distortions by) a close companion, or obscuration by arotating lumpy ring of dust orbiting the star. They are certainly noteclipsing binaries. The only possibility left seems to be non-radialpulsations, though this explanation involves difficulties of its own. Ifthey are indeed pulsating stars exhibiting non- radial gravity modes,they would be the first stars on the cool side of the Cepheidinstability strip in the Hertzsprung-Russell Diagram to be soidentified.
| Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
| The 71st Name-List of Variable Stars
Not Available
| Light Variability of HD 224639, HD 224638 and HD 224945
Not Available
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| Photometric variability of some early-type stars
Photometric observations of 12 variable early type stars are presented.The properties of individual stars are discussed, and an attempt is madeto interpret their variability. The information presented on the starsincludes the HD number and other identification, the observing runs, theperiodicity of the variations, an error estimate, and a tentativeclassification of each star.
| The frequency of Ap-stars with long rotation periods
Light variability was observed over time intervals of months to years inthe stars HD 55540, HD 71066, HD 94660, and HD 187474. The significanceof these results is discussed in terms of the frequency of chemicallypeculiar CP2 stars showing (light) variability with periods longer thanone month. This frequency, relative to the whole CP2 population, mustlie somewhere between 4 and 16 percent. Observations, properlydistributed in time, of a small subgroup of CP2 stars will be sufficientto obtain an accurate ratio of the number of LP-CP2 stars to the totalnumber of CP2 stars. These observations, when continued until theperiodicity is detected, could contribute also to the discussion whetherthese long periods should be identified with the rotation period.
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