Revised list of pulsating stars with ultra-short periods

A comprehensive list of 178 known δ Scuti and RR Lyrae-stars is presented. Using this revised list a HR diagram for these ultra short period pulsating stars is plotted and the blue and red edges of the resultant instability strip are determined. Selection effects are discussed, and the PLC relationship of Breger (1979) is tested using data from this list. Stars lying outside the defined instability region are discussed.     

On the Red Edge of the δ Scuti Instability Strip

The S Scuti star catalogue is used to derive the observational locations of such stars on the HR diagram. The theoretical and observational instability strips are compared to check the theoretical red edge obtained by considering nonlocal time-dependent convection theory. The observational instability strip almost overlaps with the theoretical one, but the observed blue and red envelopes are hotter than the theoretical edges. The distribution of S Scuti stars in the pulsation strip is not uniform.     

Pulsation in the pre-main-sequence Herbig Ae star HD 142666

Asteroseismology of pre-main-sequence δ Scuti stars has the potential not only to provide unprecedented constraints on models of these stars, but also to allow for the possibility of detecting evolutionary period changes, thus providing a direct measure of the pre-main-sequence evolutionary time-scale. In the last two years, the published number of such stars known has doubled from four to eight. Searches are now being conducted amongst the Herbig Ae stars, which are considered to be excellent candidates. We announce the discovery of δ Scuti pulsation in one Herbig Ae star, HD 142666, which lies within Marconi & Palla's theoretically predicted instability strip for pre-main-sequence stars, making this the ninth known pre-main-sequence δ Scuti star. We also demonstrate a lack of δ Scuti pulsation in another such star, HD 142527.     

Beobachtungsergebnisse der Berliner Arbeitsgemeinschaft für Veränderliche Sterne e.V. (BAV) (BAV-Mitteilungen Nr. 29)

In this 12th compilation of BAV results of observations are given from the years 1976 and 1977 for 231 observed minima of 58 eclipsing binaries, 108 maxima of 25 RR Lyrae stars, four maxima of four δ Cephei stars, four maxima of one δ Scuti star and 182 results of 23 longperiodic, semi-regular, irregular and RV Tauri stars.     

Asteroseismology of δ Scuti stars: Problems and prospects

We briefly outline the state-of-the-art seismology of δ Scuti stars from a theoretical point of view: why is it so difficult a task? The recent theoretical advances in the field that these difficulties have influenced are also discussed.     

The Nainital-Cape Survey: A search for variability in Ap and Am stars

The “Nainital-Cape Survey” program for searching photometric variability in chemically peculiar (CP) stars was initiated in 1997 at ARIES, Nainital. We present here the results obtained to date. The Am stars HD 98851, HD 102480, HD 13079 and HD 113878 were discovered to exhibit δ Scuti type variability. Photometric variability was also discovered in HD 13038, for which the type of peculiarity and variability is not fully explained. The null results of this survey are also presented and discussed.     

Abundance analysis of the γ Doradus–δ Scuti hybrid metallic line (Am) star HD 8801

Low frequency oscillation, typical for γ Doradus g‐mode type stellar core sensitive pulsation, as well as higher frequency δ Scuti type pulsation typical for p ‐modes, sensitive to the envelope, make HD 8801 a remarkable hybrid pulsator with the potential to probe a stellar structure over a wide range of radius. In addition HD 8801 is a rare pulsating metallic line (Am) star. We determined the astro‐physical fundamental parameters to locate HD 8801 in the H‐R diagram. We analyzed the element abundances, paying close attention to the errors involved, and confirm the nature of HD 8801 as a metallic line (Am) star. We also determined an upper limit on the magnetic field strength. Our abundance analysis is based on classical techniques, but uses for the final step a model atmosphere calculated with the abundances determined by us. We also discuss spectropolarimetric observations obtained for HD 8801. This object is remarkable in several respects. It is a nonmagnetic metallic line (Am) star, pulsating simultaneously in p‐ and g‐modes, but also shows oscillations with periods in between these two domains, whose excitation requires explanation. Overall, the pulsational incidence in unevolved classical Am stars is believed to be quite low; HD 8801 does not conform to this picture. Finally, about 75 % of Am stars are located in short‐period binaries, but there is no evidence that HD 8801 has a companion. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

UBVRIJH photometry of two new luminous δ Scuti stars and the discovery of δ Scuti pulsation in the most evolved Ap star known

Time-series photometry of the Hipparcos variable stars HD 199434 and 21190 is reported. Both stars are pulsators of the δ Scuti type. Reclassifications of the MK types of the stars, based on new spectrograms, are given. HD 21190 is found to be F2III SrEuSi:, making it the most evolved Ap star known. Its Strömgren photometric indices support the peculiar spectral type. It is also one of the most evolved δ Scuti stars known. Its combined Ap– δ Scuti nature makes it an important test of models of pulsation in peculiar stars recently developed by Turcotte et al., although it is more extreme than any model they examined. Physical parameters of both stars are estimated from Strömgren and H β photometry, and Hipparcos absolute magnitudes. We attempt mode identifications based on amplitude ratios and phase differences from our photometry. The dominant pulsation of HD 21190 may be an overtone radial mode. The model fits for HD 199434 are even less satisfactory, but favour an ℓ=2 mode. Given the good quality and wavelength coverage of our data, the poor results from the application of the photometric theory of mode identification may call into question the use of that technique.     

Photometry of δSct—type and Related Stars：Results of AD Ari,IP Vir and YZ Boo

Photometric results of three δ Scuti stars, AD Ari,IP Vir and YZ Boo from new observations obtained at the Xinglong Station of the Beijing Astronomical Observatory (BAO) during 2000 and 2001 are reported. We present here the preliminary analyses. Detailed studies of these stars based on additional data will be published separately.     

Study of the variability of the Delta Scuti-stars

Photoelectric observations of the Delta Scuti star KW 207 (HD 73576) are given. In spite of the low variations, the analysis of the light curves shows at least two sighificant periodicities, which seem to be related to non-radial pulsations.A third frequency, corresponding to the radial fundamental mode, is probably bame out by our data.     

Study of nonstationary processes in the close binary system RY Scuti

A new analysis is made of old electrophotometric data on RY Scuti, a close binary of an early spectral class, taken at the Abastumani Astrophysical Observatory, Georgia, during 1972–1985 and at the Maidanak Observatory, Uzbekistan, during 1979–1991. Nonstationary processes occurring from period to period, from month to month, and from year to year are identified in RY Scuti. These variations range from hundredths to tenths of a stellar magnitude. In addition, periodic changes in the light curve of this system with a period of several years have been identified near the first maximum. This result is of considerable interest in connection with similar brightness changes observed in bright blue variable LBV stars, and also is related to the ejection of a nebula surrounding the RY Scuti system. Translated from Astrofizika, Vol. 52, No. 2, pp. 275–289 (May 2009).     

Eight new δ Scuti stars

HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes.     

UBV-Beobachtungen und Periodenbestimmung für den Delta Scuti Stern HD 177392

UBV observations of the Delta Scuti type star HD 177392 were carried out in 7 neights. The three periods o⁴1215, o⁴11091, and o⁴109414 were found. These periods can not be explaine by radial pulsation.     

The delta scuti-star HD 220392: a possible component of a binary system

Physical parameters and distances are determined for the stars HD 220391 and HD 220392, which possibly form a physical pair. Ages and evolutionary masses in the new track system of Schalleret al. (1992) as well as gravitational masses of both stars are evaluated. Distance and age estimates of this possible binary system are obtained: 128(±12) pc and 7.9(±0.8) × 10⁸ yr. Both stars are located within the Delta Scuti instability strip on the H-R diagram, but a variability was only detected in HD 220392 by Lampens (1992). The pulsation mode(s) and the pulsation mass of this variable star cannot be determined at the present time.     

Discovery of 30-min oscillations in the Ap Sr(EuCr) star HD 75425

The Ap Sr(CrEu) star HD 75425 is shown to be pulsating with a 30- min period. This is unusually short for a δ Scuti star and about double the period of any known roAp star. The star is shown to be constant at the level of 0.35 mmag in the normal frequency regime of roAp pulsation (900≤ν≤ 2500 μHz). The pulsations in HD 75425 are modulated in amplitude, but the frequencies causing this modulation cannot be identified with the data in hand. HD 75425 is a very close visual double with an insecure Ap classification which needs to be reexamined. If the Ap classification of HD 75425 is correct, and the pulsations can be linked to the peculiar star, then this δ Scuti-like variability is of considerable interest. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two-site CCD observations and spectroscopy of HD 207331: A new δ Scuti variable in Cygnus

The results of an observational campaign on the new δ Scuti pulsator HD 207331 are reported. The star was observed photometrically from August 26 to September 2, 2009 from the Observatorio San Pedro Mártir (0.84-m telescope, Mexico) and the Observatorio del Teide (0.80-m telescope, Spain). An overall run of 53.8 h of useful data was collected from the two sites. Four oscillation frequencies for HD 207331 have been found above a 99% confidence level. These results confirm the multiperiodic pulsation nature of the star suggested in previous observations with sparse data. Spectroscopic observations carried out in 2009 allowed us to derive its spectral type and luminosity class as well as to estimate its rotation rate. A simple comparison with models is performed.     

A study of the variability of the Delta Scuti stars

More than 1700 photmetricV observations of the Delta Scuti HR 2557, obtained at the Merate Observatory during the two periods: 1979–80 and 1981, are analyzed. In spite of the fact that the sets of frequencies for the two periods are similar, the interpretation of these oscillations is far to be satisfactory. The lowest frequencies can be reasonably interpreted as corresponding to the lowest radial modes. Unfortunately, nothing can be said about the highest frequencies.     

On the origin of δ spots

Mount Wilson sunspot drawings from 1966 through 1980 were used in conjunction with Hα filtergrams from Big Bear Solar Observatory to examine the origin of δ spots, spots with bipolar umbrae within one penumbra. Of the six cases we studied, five were formed by the union of non-paired spots. They are either shoved into one another by two neighboring growing bipoles or by a new spot born piggy-back style on an existing spot of opposite polarity. Proper motions of the growing spots take on curvilinear paths around one another to avoid a collision. This is the shear motion observed in δ spots (Tanaka, 1979). In the remaining case, the δ spot was formed by spots that emerged as a pair. Our findings indicate no intrinsic differences in the formation or the behavior between δ spots and spots of normal magnetic configuration.     

Rapid oscillations of five stars in the spectral range A and F. I

The five stars HD 4849, HD 24712, HD 182475, HD 184552 and HD 215874 are a small group of objects enclosed in a larger observational programme for searching of rapid oscillations. They have been observed with the 50 cm ESO-telescope at La Silla (Chile). These objects are characterized as a suspected δ Scuti-type star, an Ap star, an A9 V star, an A1m star and an A9 III-IV star, respectively. For the first two stars the periods, dedected by other authors, were confirmed. For HD 182475 a period of 112.3 min has been estimated. In the case of HD 184552 an oscillation with a period of 163.3 min has been found. The star HD 215874 shows unambiguously a variation with a period of 97.2 min.     

Physical characters of HD 93044

The measurements ofuvby H of HD 93044 were obtained in April 1991, and the observational results that the star locates nearly in the middle of Scuti instability strip with somewhat deviation to red edge. According to Crawford (1979) and Philip's (1979) calibrations, the effective temperature, absolute visual magnitude and surface gravity are obtained to beT _eff = 7300±200 K,M _v = 1.^m33±0.39 and logg = 3.7±0.15, respectively. The observational results of _m1 = 0.01 give an estimate of [Fe/H] = –0.003 ± 0.18, so the opinion of metallic deficient is not supported obviously. The observations show the reddening indexE(b -y) to be 0.014 which is 1.4 times as large as the standard deviation of Crawford's (1979) statistics.Project supported by Young Foundation of Beijing Astronomical Observatory, China