내용
사진
사진 업로드
DSS Images Other Images
관련 글
UV flux distributions of γ Doradus stars
Context: It seems that the recently identified class of pulsating stars,the γ Dor type-variables, includes objects with different metalabundances and a large percentage of binaries. Aims: We looked forindicators of metal abundance peculiarities and stellar binarity in asample of 40 confirmed γ Dor stars. Methods: Absolute magnitudesfrom Hipparcos parallaxes and UV magnitudes, from the S2/S68 experimenton board the TD1 satellite, are retrieved from databases and comparedwith predicted values. A set of non variable normal stars is used tocheck the consistency of this analysis and also serve as referencestars. Results: Twenty-nine stars of the γ Dor star sample,which is 73% of it, are discovered having abnormal UV fluxes constantlyshowing UV flux excesses compared to those computed with the atmosphericparameters (Teff , log g, and metallicity) determined fromcalibration of the uvbyβ indices. The reason for this UV excess offlux at 196.5 nm and at 236.5 nm, which was previously known only for HD209295, cannot be ascribed to binarity alone. An extra source of UV fluxor less UV absorption - yet unknown - must be present.Tables 1-3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/472/241
| Progenitors of type Ia supernovae: Binary stars with white dwarf companions
Type Ia SNe (SNe Ia) are thought to come from carbon oxygen white dwarfsthat accrete mass from binary companions until they approach theChandrasekhar limit, ignite carbon, and undergo complete thermonucleardisruption. A survey of the observed types of binaries that containwhite dwarfs is presented. We propose that certain systems that seemmost promising as SN Ia progenitors should be more intensively observedand modeled, to determine whether the white dwarfs in these systems willbe able to reach the Chandrasekhar limit. In view of the number ofpromising single-degenerate systems and the dearth of promisingdouble-degenerate systems, we suspect that single-degenerates producemost or perhaps all SNe Ia, while double-degenerates produce some orperhaps none.
| Variable Stars in the Open Cluster NGC 2099 (M37)
Time-series CCD photometric observations of the intermediate-age opencluster NGC 2099 were performed to search for variable stars. We alsocarried out BV photometry to study physical properties of variables inthe cluster. Using V-band time-series data, we carefully examined lightvariations of about 12,000 stars in the range of 10
| Rotational velocities of A-type stars. III. Velocity distributions
Aims.A sample of v sin i of B9 to F2-type main sequence single stars hasbeen built from highly homogeneous {v sin i} parameters determined for alarge sample cleansed of objects presenting the Am and Ap phenomenon aswell as of all known binaries. The aim is to study the distributions ofrotational velocities in the mass range of A-type stars for normalsingle objects. Methods: .Robust statistical methods are used torectify the {v sin i} distributions for the projection effect and theerror distribution. The equatorial velocity distributions are obtainedfor about 1100 stars divided in six groups defined by the spectral type,under the assumption of randomly orientated rotational axes.Results: .We show that late B and early A-type main-sequence stars havegenuine bimodal distributions of true equatorial rotational velocitiesprobably due to angular momentum loss and redistribution that the starunderwent before reaching the main sequence. A striking lack of slowrotators is noticed among intermediate and late A-type stars.Full Table [see full text] is only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/671 Appendices areonly available in electronic form at http://www.aanda.org
| Discovery of hybrid γ Dor and δ Sct pulsations in BD+18 4914 through MOST spacebased photometry
We present a total of 57 days of contiguous, high-cadence photometry (14days in 2004 and 43 in 2005) of the star BD+18 4914 obtained with theMOST1 satellite. We detect 16 frequencies down to a signal-to-noise of3.6 (amplitude 0.5 mmag). Six of these are less than 3 cycles/day, andthe other ten are between 7 and 16 cycles/day. We intrepret the lowfrequencies as g-mode γ Doradus-type pulsations and the others asδ Scuti-type p-modes, making BD+18 4914 one of the few knownhybrid pulsators of its class. If the g-mode pulsations arehigh-overtone non-radial modes with identical low degree, we can assigna unique mode classification of n={12, 20, 21, 22, 31, 38} based on thefrequency ratio method.
| HD 114839 - An Am star showing both δ Scuti and γ Dor pulsations discovered through MOST photometry
Using MOST1 (Microvariability and Oscillations of STars) satellite guidestar photometry, we have discovered a metallic A star showing hybrid p-and gmode pulsations. HD 114839 was observed nearly continuously for 10days in March, 2005. We identify frequencies in three groups: the firstcentered near 2 cycles/day, in the γ Dor pulsation range, and twoothers near 8 and 20, both in the δ Scuti range. This is only thefourth known such hybrid pulsator, including another MOST discovery(Rowe et al. 2006).
| The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Non-radial pulsations in the γ Doradus star HD 195068
We present high resolution spectroscopic observations of the γDoradus star HD 195068. About 230 spectra werecollected over 2 years. Time series analysis performed on radialvelocity data shows a main peak at 1.61 d-1 , a frequency notyet detected in photometry. The Hipparcos photometric 1.25d-1 frequency is easily recovered as is 1.30 d-1while the third photometric frequency, 0.97 d-1 , is onlymarginally present. The good quality of our data, which includes 196spectra collected over seven consecutive nights, shows that both the1.61 d-1 and intermediate 1.27 d-1 (mixture of1.25 and 1.30 d-1 ) frequencies are present in the lineprofile variations. Using the Fourier-Doppler Imaging (FDI) method, thevariability associated with 1.61 d-1 can be successfullymodeled by a non-radial pulsation mode ℓ=5± 1, |m|=4±1. For the intermediate frequency 1.27 d-1 we deduceℓ=4± 1, |m|=3± 1. Evidence that the star is notpulsating in the radial mode (ℓ=0) rules out a previousclassification as an RR Lyrae type star. We investigate the timevariability of FDI power spectra concluding that the observed temporalvariability of modes can be explained by a beating phenomenon betweenclosely spaced frequencies of two non-radial modes. The distribution ofthe oscillation power within the line profile indicates that there is asignificant tangential velocity component of oscillations characteristicof high radial order gravity modes which are predicted to be observed inγ Doradus type stars.
| The frequency ratio method and the new multiperiodic γ Doradus star HD 218427
Oscillations of γ Dor-type were discovered in the star HD 218427through simultaneous uvby photometric observations carried out in theyear 2003. A few Hβ-Crawford measurements were also collected forcalibration purposes and they locate this star well inside the γDor instability region. We find HD 218427 to be deficient in metals,similar to other well-defined γ Dor stars, and discuss thepossibility that it has a λ Boo nature. We carried out frequencyanalysis for different filters, including the combined "vby" filter, andfive frequencies were found as significant with periods ranging between0.3 and 0.8 days. The recently-developed frequency ratio method is usedin order to identify the excited modes. The results are consistent withan l=2 identification for all the modes and with high radial quantumnumbers (n40) for the three main observed periodicities. Thepossibility of multiplet structures is also discussed. However, noconsistency is found when using the time-dependent convection treatmentto discriminate modes. This disagreement can be due to the largerotation velocity taking place in HD 218427 and, consequently, thesignificant coupling between the modes.
| A spectroscopic study of southern (candidate) γ Doradus stars. I. Time series analysis
We present the results of a spectroscopic study of 37 southern(candidate) γ Doradus stars based on échelle spectra. Theobserved spectra were cross-correlated with the standard templatespectrum of an F0-type star for easier detection of binary and intrinsicvariations. We identified 15 objects as spectroscopic binaries,including 7 new ones, while another 3 objects are binary suspects. Atleast 12 objects show composite spectra. We could determine the orbitalparameters for 9 binaries, of which 4 turned out to be ellipsoidalvariables. For 6 binaries, we estimated the expected time-base of theorbital variations. Clear profile variations were observed for 17objects, pointing towards stellar pulsation. For 8 of them, we haveevidence that the main spectroscopic and photometric periods coincide.Our results, in combination with prior knowledge from the literature,lead to the classification of 10 objects as new bona fide γDoradus stars, 1 object as a new bona fide δ Scuti star, and 8objects as constant stars. Finally, we determined the projectedrotational velocity by two independent methods. The resulting v sin ivalues range from 3 to 135 {km s-1}. For the bona fideγ Doradus stars, the majority has v sin i below 60 {kms-1}.
| Fourier-Doppler imaging of non-radial pulsations in gamma Doradus stars .
This paper deals with a class of non-radial pulsators along the mainsequence, namely the gamma Doradus stars for which much effort iscurrently made in order to constrain their pulsation characteristics.However, because of their relatively low amplitude (few tens of mmag inphotometry) and due to the long time scales of the variation (between0.3 and 3 days), the detection and identification of their pulsations israther difficult, using the photometric data only. Consequently, thespectroscopic studies of the stars having well-known photometricproperties are very valuable and we study in detail the line profilevariability (LPV) in gamma Doradus candidates observed at Observatoirede Haute-Provence during a two-year high-resolution spectroscopycampaign. The non-radial behavior of selected stars is revealed with theadvent of Doppler Mapping and two-dimensional Fourier-Doppler Imagingmethods for line-profile analysis, which allowed us to detect andidentify the pulsation modes described below.
| Theoretical Aspects of g-mode Pulsations in gamma Doradus Stars
gamma Dor stars are main sequence variable A-F stars whose long periods(between 0.35 and 3 days) correspond to high-order gravity modespulsation. Most of them are multiperiodic. We will concentrate here ontwo theoretical aspects of these stars. First, an analysis of thedriving mechanism of the gamma Dor g-modes is presented, using thelinear Time-Dependent Convection (TDC) treatment of Gabriel\cite{Gabriel1996} and Grigahcène et al. \cite{Grigahcene}. Thisdriving is due to a periodic flux blocking mechanism at the base oftheir convective envelope. The location of the blue and red edges oftheir instability strip as well as the periods range of their observedmodes is explained by the balance between this driving mechanism andradiative damping in the g-mode cavity. Secondly, the multi-colorphotometric amplitude ratios and the phase differences between the lightand velocity curves are considered. It is shown that the agreementbetween theory and observations obtained with TDC models is much betterthan with Frozen Convection (FC) models. The theoretical analysis ofthese observables makes the photometric identification of the degreeℓ of the modes possible and gives constraints on the characteristicsof the convective envelope of these stars. Finally, the attractivepotential of gamma Dor stars as targets for asteroseismology isconsidered.
| Observational results for northern and southern (candidate) gamma Doradus stars .
We report on observational results obtained for 78 objects originallyclassified as bona-fide or candidate gamma Doradus stars. For thesouthern objects, we gathered echelle spectra with the CORALIEspectrograph attached to the Euler telescope in 1998-2003 and/orJohnson-Cousins B,V,I_c observations with the MODULAR photometerattached to the 0.5-m SAAO telescope in 1999-2000. For the northernobjects, we obtained Geneva U,B,B_1,B_2,V,V_1,G observations with the P7photometer attached to the 1.2-m Mercator telescope in 2001-2004. Atleast 15 of our objects are binaries, of which 7 are new. For 6binaries, we determined the orbit for the first time. At least 17objects show profile variations and at least 12 objects aremultiperiodic photometric variables. Our results allow us to upgrade 11objects to bona-fide gamma Doradus stars and to downgrade 8 objects toconstant up to the current detection limits. Mode identification isstill ongoing, but so far, only ℓ = 1 and 2 modes have beenidentified.
| The orbit of the close spectroscopic binary \varepsilon Lup and the intrinsic variability of its early B-type components
We subjected 106 new high-resolution spectra of the double-linedspectroscopic close binary \varepsilon Lup, obtained in a time-span of17 days from two different observatories, to a detailed study of orbitaland intrinsic variations. We derived accurate values of the orbitalparameters. We refined the sidereal orbital period to 4.55970d days andthe eccentricity to e=0.277. By adding old radial velocities, wediscovered the presence of apsidal motion with a period of the rotationof apses of about 430 years. Such a value agrees with theoreticalexpectations. Additional data is needed to confirm and refine thisvalue. Our dataset did not allow us to derive the orbit of the thirdbody, which is known to orbit the close system in 64 years. We presentthe secondary of \varepsilon Lup as a new β Cephei variable, whilethe primary is a β Cephei suspect. A first detailed analysis ofline-profile variations of both primary and secondary led to detectionof one pulsation frequency near 10.36 c d-1 in thevariability of the secondary, while no clear periodicity was found inthe primary, although low-amplitude periodicities are still suspected.The limited accuracy and extent of our dataset did not allow any furtheranalysis, such as mode-identification.
| Asteroseismology of Delta Scuti and Gamma Doradus Stars
We give an overview of past and present efforts to make seismology ofδ Scuti and γ Doradus stars possible. Previous work has notled to the observational detection and identification of a sufficientnumber of pulsation modes for these pulsators for the construction ofunique seis-mic models. However, recent efforts including largeground-based obser-vational campaigns, work on pre-main sequencepulsators, asteroseismic satellite missions, theoretical advances onmode identification methods, and the discovery of a star showingsimultaneous self-excited δ Scuti and γ Doradus oscillationssuggest that we may be able to explore the interiors of these pulsatorsin the very near future.
| Eleven New γ Doradus Stars
We present new high-dispersion spectroscopic and precise photometricobservations to identify 11 new γ Doradus variables. Seven ofthese new γ Doradus stars appear to be single, three are primariesof single-lined binaries, and one has two distant visual companions;none are double-lined or close visual binaries. Several of the starsshow spectroscopic line-profile and low-amplitude radial velocityvariability indicative of pulsation. All 11 stars are photometricallyvariable with amplitudes between 8 and 93 mmag in Johnson B and periodsbetween 0.398 and 2.454 days. One star is monoperiodic; the rest havebetween two and five independent periods. The variability at all periodsapproximates a sinusoid, although three of the stars exhibitcycle-to-cycle variation in the level of maximum brightness, similar tothe Blazhko effect observed in some RR Lyrae stars. We provide a newtabulation of all 54 γ Doradus stars confirmed to date and listsome of their properties. All are dwarfs or subgiants and lie within awell-defined region of the H-R diagram that overlaps the cool edge ofthe δ Scuti instability strip. Four of the new γ Doradusvariables from this paper also lie within the δ Scuti instabilitystrip but do not exhibit the additional higher frequency variabilitytypical of δ Scuti stars. The variability type of several of thesestars given in the General Catalog of Variable Stars and in SIMBADshould now be revised.
| Convection-pulsation coupling. II. Excitation and stabilization mechanisms in δ Sct and γ Dor stars
We apply here the Time Dependent Convection (TDC) treatment presented inour earlier paper in this series to the study of δ Sct and γDor pulsating stars. Stabilization of the δ Sct p-modes at the rededge of the Instability Strip (IS) and the driving of the γ Dorg-modes are explained by our models. Theoretical IS obtained withdifferent values of the Mixing Length (ML) parameter α arecompared to observations and a good agreement is obtained for αbetween 1.8 and 2. The influence of each term of our TDC treatment(perturbation of convective flux, turbulent pressure, and turbulentkinetic energy dissipation) on the eigenfrequencies and on the drivingand damping mechanisms is investigated. Finally, we show that our TDCmodels predict the likely existence of hybrid stars with both δSct p-modes and γ Dor g-modes oscillations.
| HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations
We have discovered the first example of a star pulsating intrinsicallywith both γ Doradus and δ Scuti frequencies. The star, HD8801, is an Am metallic-line star that appears to be single. Since thevast majority of Am stars are members of binary systems with periodsless than 1000 days and also do not pulsate, HD 8801 possesses a veryunusual, if not unique, combination of physical properties. Ourphotometry, acquired with an automatic telescope at FairbornObservatory, resolves six independent pulsation periods between 0.048and 0.404 days. The two longest periods lie within the range of γDor variables, while the four shorter periods are within the range ofδ Sct stars. Eleven radial velocities, obtained over an 11 monthperiod, have a mean of 0.8+/-0.3 km s-1, providing noevidence for a spectroscopic companion. The star is on the main sequenceand lies within both the γ Dor and δ Sct instability strips.Pulsation constants computed for the six periods agree with pulsationconstants computed for other γ Dor and δ Sct variables. HD8801 is also the first confirmed case of a metallic-line star pulsatingwith γ Dor frequencies. Its projected rotational velocity of 55 kms-1 is typical for Am stars, which, as a group, rotate moreslowly than normal A stars. HD 8801's slow rotation compared to normal Astars does not appear to arise from either a binary companion orevolutionary expansion and thus remains a puzzle. The coexistence ofmetallicism and pulsation in several main-sequence stars near the rededge of the δ Sct strip contradicts recent models that predictpulsations only in more evolved stars.
| Interpretation of the variability of the β Cephei star λ Scorpii. I. The multiple character
We derive accurate values of the orbital parameters of the close binaryβ Cephei star λ Scorpii. Moreover, we present the firstdetermination of the properties of the triple system to which λScorpii belongs. Our analysis is based on a time series of 815high-resolution spectra, covering a timespan of 14 years. We find aclose orbit of 5.9525 d days (e=0.26) and a wide orbit of approximately1082d days (e=0.23). The orbital parameters of the triplestar and a spectrum synthesis lead us to conclude that the system iscomposed of two early-type B stars and a low-mass pre-main-sequence starrather than containing an ultra-massive white dwarf as claimed before.Our proposed configuration is compatible with population synthesis. Theradial velocity variations of the primary allow us to confirm thepresence of at least one pulsation mode with frequency 4.679410 cd-1 which is subject to the light-time effect in the triplesystem. A detailed analysis of the complex line-profile variations isdescribed in a subsequent paper.Based on observations obtained with the Coudé EchelleSpectrograph on the ESO CAT telescope and with the CORALIE EchelleSpectrograph on the 1.2-m Euler Swiss telescope, both situated at LaSilla, ChileTable \ref{observations} is only available in electronic form athttp://www.edpsciences.org
| SX Phoenicis Stars in the Globular Cluster NGC 5466
Through time-series CCD photometry of the globular cluster NGC 5466, wehave detected nine SX Phoenicis stars, including three new ones. All theSX Phoenicis stars are located in the blue straggler region in thecolor-magnitude diagram of NGC 5466. Five of them clearly showdouble-radial mode features, the periods of which are consistent withthe theoretical ratio of the first-overtone mode to the fundamental mode(P1H/PF). Normally, it has not been easy to securea P-L relation for the SX Phoenicis stars because their pulsational modehas been difficult to determine. The existence of five SX Phoenicisstars in NGC 5466 with double-radial modes allows us to reliably derivea P-L relation for the fundamental mode of SX Phoenicis stars. Usingseven SX Phoenicis stars, including five stars with double-radial modes,we derive a P-L relation for the fundamental mode in NGC 5466,=-3.25(+/-0.46)logP+14.70(+/-0.06),(σ=+/-0.04),corresponding to =-3.25(+/-0.46)logP-1.30(+/-0.06)for an adopted distance modulus of (m-M)0=16.00 and zeroreddening.
| HD 207651: A Triple System with δ Scuti and Ellipsoidal Variations But No γ Doradus Pulsations
We examine HD 207651 as a possible example of a star exhibiting bothγ Doradus and δ Scuti type pulsations. We find photometricperiods of 0.06479 and 0.06337 days with peak-to-peak amplitudes inJohnson B of 21 and 13 mmag, respectively, clearly indicating δScuti pulsations. Additional light variation with a period of 0.73540days and an even larger amplitude of 31 mmag is within the range ofγ Doradus pulsation periods but results instead from theellipticity effect. HD 207651 has a composite spectrum with a weak,narrow absorption line superposed near the center of each broad metalline. The broad-lined component is the primary of a short-period,single-lined binary, which has a period of 1.4708 days, twice the periodof the ellipsoidal variations seen in the photometry. We determine theprimary to be an A8 giant and estimate the unseen secondary of theshort-period binary to be a mid-M dwarf. The narrow-lined star, an F7:dwarf, shows velocity variability with a period of months or perhapsyears. It is thus a more distant companion to the binary, making HD207651 a triple system. All light variations come from the A8 giantprimary star. Since the 0.73540 day variation results from theellipticity effect, HD 207651 is not an example of a star that exhibitsboth δ Scuti and γ Doradus pulsations. The growing number ofconfirmed γ Doradus stars that also occur within the δ Scutiinstability strip but fail to show additional δ Scuti variabilitymakes it increasingly unlikely that the two types of pulsation cancoexist in the same star.
| Asteroseismology of the β Cephei star ν Eridani - I. Photometric observations and pulsational frequency analysis
We undertook a multisite photometric campaign for the β Cephei starν Eridani. More than 600 h of differential photoelectric uvyVphotometry were obtained with 11 telescopes during 148 clear nights.The frequency analysis of our measurements shows that the variability ofν Eri can be decomposed into 23 sinusoidal components, eight of whichcorrespond to independent pulsation frequencies between 5 and 8cd-1. Some of these are arranged in multiplets, whichsuggests rotational m-mode splitting of non-radial pulsation modes asthe cause. If so, the rotation period of the star must be between 30 and60 d.One of the signals in the light curves of ν Eri has a very lowfrequency of 0.432 cd-1. It can be a high-order combinationfrequency or, more likely, an independent pulsation mode. In the lattercase, ν Eri would be both a β Cephei star and a slowly pulsatingB (SPB) star.The photometric amplitudes of the individual pulsation modes of ν Eriappear to have increased by about 20 per cent over the last 40 years. Sohave the amplitudes of the dominant combination frequencies of the star.Among the latter, we could only identify sum frequencies with certainty,not difference frequencies, which suggests that neither light-curvedistortion in its simplest form nor resonant mode coupling is theirsingle cause.One of our comparison stars, μ Eridani, turned out to be variablewith a dominant time-scale of 1.62 d. We believe either that it is anSPB star just leaving its instability strip or that its variations areof rotational origin.
| 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.
| Astrophysics in 2002
This has been the Year of the Baryon. Some low temperature ones wereseen at high redshift, some high temperature ones were seen at lowredshift, and some cooling ones were (probably) reheated. Astronomerssaw the back of the Sun (which is also made of baryons), a possiblesolution to the problem of ejection of material by Type II supernovae(in which neutrinos push out baryons), the production of R CoronaeBorealis stars (previously-owned baryons), and perhaps found the missingsatellite galaxies (whose failing is that they have no baryons). A fewquestions were left unanswered for next year, and an attempt is made todiscuss these as well.
| Spectroscopy of Early F Stars: γ Doradus Candidates and Possible Metallic Shell Stars
We obtained high-resolution spectroscopic observations of 34 γDoradus candidates. From the red-wavelength spectra, we determinedspectral classes, radial velocities, and projected rotationalvelocities. The spectra of seven late A or early F stars show metalliclines that have composite profiles consisting of a narrow component nearthe center of a broad line, indicating that they may be shell stars orbinaries. Several stars, including HD 152896, HD 173977, HD 175337, andHD 195068/9, show large line profile asymmetries. Two stars, HD 11443(=α Trianguli) and HD 149420, are ellipsoidal variables and notγ Doradus stars. The percentage of binary systems in our samplemay be as high as 74%.
| The Orbit and Pulsation Periods of the γ Doradus Variable HR 6844 (V2502 Ophiuchi)
We obtained spectroscopic and photometric observations of the γDoradus variable HR 6844 (=V2502 Ophiuchi). Radial velocities show thatthis star is a single-lined binary with a period of 4.4852 days. Theprimary is an F1 V star, while the secondary is likely an M dwarf.Velocity residuals to a circular orbit have a period of 1.3071 days andan amplitude of ~3 km s-1. Three periods of light variationwere detected, 1.30702, 1.4350, and 0.62286 days. The first period isessentially identical to that found in the radial velocities and has thelargest amplitude, a peak-to-peak value of 0.067 mag in B. Thephotometric check star, 73 Oph (=HR 6795), has light variations with aperiod of 0.61439 in B. Although the star is a close visual binary, thelight variations are ascribed to the primary, making it most likely anewly discovered γ Doradus variable.
| The mass of the neutron star in Vela X-1 and tidally induced non-radial oscillations in GP Vel
We report new radial velocity observations of GP Vel / HD 77581, theoptical companion to the eclipsing X-ray pulsar Vela X-1. Using dataspanning more than two complete orbits of the system, we detect evidencefor tidally induced non-radial oscillations on the surface of GP Vel,apparent as peaks in the power spectrum of the residuals to the radialvelocity curve fit. By removing the effect of these oscillations (tofirst order) and binning the radial velocities, we have determined thesemi-amplitude of the radial velocity curve of GP Vel to beKo = 22.6 +/- 1.5 km s-1. Given the accuratelymeasured semi-amplitude of the pulsar's orbit, the mass ratio of thesystem is 0.081 +/- 0.005. We are able to set upper and lower limits onthe masses of the component stars as follows. Assuming GP Vel fills itsRoche lobe then the inclination angle of the system, i, is70.1deg +/- 2.6deg. In this case we obtain themasses of the two stars as Mx = 2.27 +/- 0.17 Msunfor the neutron star and Mo = 27.9 +/- 1.3 Msunfor GP Vel. Conversely, assuming the inclination angle isi=90deg, the ratio of the radius of GP Vel to the radius ofits Roche lobe is beta = 0.89 +/- 0.03 and the masses of the two starsare Mx = 1.88 +/- 0.13 Msun and Mo =23.1 +/- 0.2 Msun. A range of solutions between these twosets of limits is also possible, corresponding to other combinations ofi and beta . In addition, we note that if the zero phase of the radialvelocity curve is allowed as a free parameter, rather than constrainedby the X-ray ephemeris, a significantly improved fit is obtained with anamplitude of 21.2 +/- 0.7 km s-1 and a phase shift of 0.033+/- 0.007 in true anomaly. The apparent shift in the zero phase of theradial velocity curve may indicate the presence of an additional radialvelocity component at the orbital period. This may be anothermanifestation of the tidally induced non-radial oscillations andprovides an additional source of uncertainty in the determination of theorbital radial velocity amplitude.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| 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.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
