Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
The Nainital-Cape Survey. II. Report for pulsation in five chemically peculiar A-type stars and presentation of 140 null results
Aims.We search for photometric variability in chemically peculiar A typestars in the northern hemisphere. Methods: .High-speed photometricobservations of Ap and Am star candidates have been carried out fromARIES (Manora Peak, Nainital) using a three-channel fast photometerattached to the ARIES 104-cm Sampurnanand telescope. Results:.This paper presents three new variables: HD 113878, HD 118660 and HD207561. During the time span of the survey (1999 December to 2004January) pulsations of the δ Sct type were also found for the twoevolved Am stars HD 102480 and HD 98851, as reported in Joshi et al.(2002, 2003). Additionally, we present 140 null results of the surveyfor this time span. Conclusions: .The star HD 113878 pulsates witha period of 2.31 h, which is typical of δ Sct stars. HD 118660exhibits multi-periodic variability with a prominent period of nearly 1h. These periods need to be investigated and make HD 118660 aparticularly interesting target for further observations. For HD 207561,a star classified as Am, a probable pulsation with a period of 6 min wasfound in the light curves obtained on two consecutive nights. Both HD102480 and HD 98851 exhibit unusual alternating high and low amplitudemaxima, with a period ratio of 2:1. The analysis of the null resultsconfirms the photometric quality of the Nainital site.
| Studies of chemically peculiar stars
This thesis is on the framework of the "NainiTal-Cape Survey" programmefor searching photometric variability in chemically peculiar stars,initiated in 1997 at the ARIES, NainiTal, India, in collaboration withthe South African Astronomical Observatory, Cape Town and ISRO,Bangalore. This paper presents the corresponding results. The Am starsHD98851, HD102480, HD13079 and HD113878 were discovered to exhibit aScuti type of variability. Photometric variability was also discoveredin HD13038, for which the type of peculiarity and variability is not yetfully explained. The null results obtained in this survey are alsopresented and discussed, as they provide an interesting data referencefor upcoming studies.
| The Nainital-Cape Survey: A Search for Variability in Ap and Am Stars
The "Nainital-Cape Survey" program for searching photo-metricvariability in chemically peculiar (CP) stars was initiated in 1997 atARIES, Nainital. We present here the results obtained to date. The Amstars HD98851, HD102480, HD13079 and HD113878 were discovered to exhibitδ Scuti type variability. Photometric variability was alsodis-covered in HD13038, for which the type of peculiarity andvariability is not fully explained. The null results of this survey arealso presented and discussed.
| 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.
| Discovery of unusual pulsations in the cool, evolved Am stars HD 98851 and HD 102480
The chemically peculiar (CP) stars HD 98851 and HD 102480 have beendiscovered to be unusual pulsators during the `Naini Tal-Cape Survey'programme to search for pulsational variability in CP stars. Time seriesphotometric and spectroscopic observations of these newly discoveredstars are reported here. Fourier analyses of the time series photometryreveal that HD 98851 is pulsating mainly with frequencies 0.208 and0.103 mHz, and HD 102480 is pulsating with frequencies 0.107, 0.156 and0.198 mHz. The frequency identifications are all subject to 1d-1 cycle count ambiguities. We have matched the observedlow-resolution spectra of HD 98851 and HD 102480 in the range 3500-7400Å with theoretical synthetic spectra using Kurucz models withsolar metallicity and a micro-turbulent velocity of 2 km s-1.These yield Teff= 7000 +/- 250 K, log g= 3.5 +/- 0.5 for HD98851 and Teff= 6750 +/- 250 K, log g= 3.0 +/- 0.5 for HD102480. We determined the equivalent H-line spectral class of thesestars to be F1 IV and F3 III/IV, respectively. A comparison of thelocation of HD 98851 and HD 102480 in the HR diagram with theoreticalstellar evolutionary tracks indicates that both stars are about1-Gyr-old, 2-Msolar stars that lie towards the red edge ofthe δ Sct instability strip. From comparison between the observedand calculated physical parameters, we conclude that HD 98851 and HD102480 are cool, evolved Am pulsators. The light curves of thesepulsating stars have alternating high and low amplitudes, nearlyharmonic (or subharmonic) period ratios, high pulsational overtones andAm spectral types. This is unusual for both Am and δ Sctpulsators, making these stars interesting objects for furtherobservational and theoretical studies.
| On the Red Edge of the δ Scuti Instability Strip
The δ Scuti star catalogue is used to derive the observationallocations of such stars on the HR diagram. The theoretical andobservational instability strips are compared to check the theoreticalred edge obtained by considering non-local time-dependent convectiontheory. The observational instability strip almost overlaps with thetheoretical one, but the observed blue and red envelopes are hotter thanthe theoretical edges. The distribution of δ Scuti stars in thepulsation strip is not uniform.
| New pulsating variables discovered from the Naini Tal-Cape survey.
Not Available
| Naini Tal-Cape survey for pulsating chemically peculiar stars - A status report
The "Naini Tal-Cape survey for rapidly oscillating Ap stars", to searchthe northern hemi-sphere sky for pulsating stars was initiated in 1997.This is a collaboration between India and South Africa. So far about 70stars have been observed and 4 variables have been discovered. Thevariables are HD 13079, HD 13038, HD 12098 and HD 98851. Of these HD12098 is a likely rapidly oscillating Ap star. This paper gives a statusreport on the survey. The methodology of this survey and an evaluationof observing time vis-a-vis the chance of discovering a new variable arediscussed.
| The 76th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1406 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| The Naini Tal - Cape survey for pulsations in chemically peculiar A-type stars. I. Methods and preliminary results
A new survey for pulsating, chemically peculiar A- and F-type stars inthe northern hemisphere has been initiated using the 1-m telescope atUttar Pradesh State Observatory in Naini Tal. The survey is primarilystructured to reveal high-overtone pulsations in chemically peculiar A-Fstars, but it is also revealing low-overtone delta Scuti-type pulsationsin stars with peculiar colours. This paper describes the scope andmethods of the survey. Preliminary observations of 28 candidate starsare presented and the discovery of three new pulsators, HD 12098, HD13038 and HD 13079, is announced. Null results for the remaining 25stars are also discussed.
| Survey for roAp stars in the northern sky from Naini Tal
Of the 31 known rapidly oscillating Ap (roAp) stars, 28 are in thesouthern sky and majority of them were discovered at SAAO indicatingthat a systematic survey also is needed in the northern sky. Therefore,a project has been initiated at the Uttar Pradesh State Observatory inNaini Tal with the objective to find and study new roAp stars in thenorthern sky. The test observing campaigns were made during 1997 and1998 from UPSO at Naini Tal. A brief report of these efforts ispresented here. The initial results were encouraging and qualified thesite, the telescope and the instrument as the right combination neededfor the success of the project. Though these preliminary observationsdid not yield new roAp stars, they did lead to the discovery of deltaScuti pulsations in two chemically peculiar stars, HD 13079 and HD13038.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Observing roAp Stars with WET: A Primer
We give an extensive primer on roAp stars -- introducing them, puttingthem in context and explaining terminology and jargon, and giving athorough discussion of what is known and not known about them. Thisprovides a good understanding of the kind of science WET could extractfrom these stars. We also discuss the many potential pitfalls andproblems in high-precision photometry. Finally, we suggest a WETcampaign for the roAp star HR 1217.
| Discovery of pulsations in the AM star HD 13079
Pulsation in cool main-sequence Am stars is a rare phenomenon observedin a few marginal Am stars and only one classical Am star. Thechemically peculiar star HD 13079 is shown to be pulsating with a 78-minperiod and a peak-to-peak B amplitude of 0.02mag. The Hipparcosparallax, uvbyβ photometry and pulsations together suggest that HD13079 is an Am star near the zero-age main sequence, and that it is afundamental-mode pulsator on the red edge of the instability strip.
| Discovery of pulsations in the double star HD 13079
Not Available
| A preliminary compilation of DS-programme star positions
A catalog is presented of the double-star-program (DS-program) starpositions, listing right ascensions for 930 DSs and declinations for1225 DSs of the program. The positions were compiled from the observedvalues obtained between 1980 and 1987 with the meridian circles of sixUSSR observatories (the Moscow, Kazan', Kiev, Khar'kov, Odessa, andTashkent Observatories) and the Belgrade Observatory. The measurementsand the treatment of the observational material were performed using therelative method, and the FK-4 system stars were used as reference stars.
| Mesures d'etoiles doubles faites a Nice.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...33..275M&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Zincirli Prenses |
| Sað Açýklýk: | 02h09m02.33s |
| Yükselim: | +39°35'32.3" |
| Görünürdeki Parlaklýk: | 8.898 |
| Uzaklýk: | 181.159 parsek |
| özdevim Sað Açýklýk: | 14.9 |
| özdevim Yükselim: | -11.1 |
| B-T magnitude: | 9.287 |
| V-T magnitude: | 8.931 |
Kataloglar ve belirtme:
|
