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تسجيل مستخدم جديدDiscovery of {delta} Scuti Pulsations in the Young Hybrid Debris Disk Star HD 156623
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The bRing robotic observatory network was built to search for circumplanetary material within the transiting Hill sphere of the exoplanet $beta$ Pic b across its bright host star $beta$ Pic. During the bRing survey of $beta$ Pic, it simultaneously monitored the brightnesses of thousands of bright stars in the southern sky ($V$ $simeq$ 4-8, $delta$ $lesssim$ -30$^{circ}$). In this work, we announce the discovery of $delta$ Scuti pulsations in the A-type star HD 156623 using bRing data. HD 156623 is notable as it is a well-studied young star with a dusty and gas-rich debris disk, previously detected using ALMA. We present the observational results on the pulsation periods and amplitudes for HD 156623, discuss its evolutionary status, and provide further constraints on its nature and age. We find strong evidence of frequency regularity and grouping. We do not find evidence of frequency, amplitude, or phase modulation for any of the frequencies over the course of the observations. We show that HD 156623 is consistent with other hot and high frequency pre-MS and early ZAMS $delta$ Scutis as predicted by theoretical models and corresponding evolutionary tracks, although we observe that HD 156623 lies hotter than the theoretical blue edge of the classical instability strip. This, coupled with our characterization and Sco-Cen membership analyses, suggest that the star is most likely an outlying ZAMS member of the $sim$16 Myr Upper Centaurus-Lupus subgroup of the Sco-Cen association.
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Hybrid stars of the {gamma} Doradus and {delta} Scuti pulsation types have great potential for asteroseismic analysis to explore their interior structure. To achieve this, mode identi- fications of pulsational frequencies observed in the stars must b
e made, a task which is far from simple. In this work we begin the analysis by scrutinizing the frequencies found in the CoRoT photometric satellite measurements and ground-based high-resolution spectroscopy of the hybrid star HD 49434. The results show almost no consistency between the frequencies found using the two techniques and no characteristic period spacings or couplings were identified in either dataset. The spectroscopic data additionally show no evidence for any long term (5 year) variation in the dominant frequency. The 31 spectroscopic frequencies identified have standard deviation profiles suggesting multiple modes sharing (l, m) in the {delta} Scuti frequency region and several skewed modes sharing the same (l, m) in the {gamma} Doradus frequency region. In addition, there is a clear frequency in the {gamma} Doradus frequency region that appears to be unrelated to the others. We conclude HD 49434 remains a {delta} Scuti/ {gamma} Doradus candidate hybrid star but more sophisticated models dealing with rotation are sought to obtain a clear picture of the pulsational behaviour of this star.
Low frequency oscillation, typical for Gamma Doradus g-mode type stellar core sensitive pulsation, as well as higher frequency Delta Scuti type pulsation typical for p-modes, sensitive to the envelope, make HD 8801 a remarkable hybrid pulsator with t
he 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 astrophysical fundamental parameters to locate HD 8801 in the HR 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 non-magnetic 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.
Preliminary results on the discovery and follow-up observations of a new $delta$ Scuti pulsator in the Cygnus field are presented. The variability of the star HD 207331 was detected while testing a Stromgren spectrophotometer attached to the H.L. Joh
nson 1.5-m telescope at the San Pedro Martir observatory, Mexico. CCD photometric data acquired soon after confirmed its variability. A few hours of $uvby$ differential photoelectric photometry during three nights revealed at least two beating periods. A two-site observational campaign carried out during one week in 2009 confirms the multi-periodic nature of this new $delta$ Scuti pulsator.
MOST observations and model analysis of the Herbig Ae star HD 34282 (V1366 Ori) reveal {delta}-Scuti pulsations. 22 frequencies are observed, 10 of which confirm those previously identified by Amado et al. (2006), and 12 of which are newly discovered
in this work. We show that the weighted-average frequency in each group fits the radial p-mode frequencies of viable models. We argue that the observed pulsation spectrum extends just to the edge to the acoustic cut-off frequency and show that this also is consistent with our best-fitting models.
We concentrate on an asteroseismological study of HD 261711, a rather hot delta Scuti type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD 261711 was discovered to be a pre-main sequence de
lta Scuti star using the time series photometry obtained by the MOST satellite in 2006. High-precision, time-series photometry of HD 261711 was obtained by the MOST and CoRoT satellites in 4 separate new observing runs that are put into context with the stars fundamental atmospheric parameters obtained from spectroscopy. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new delta Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group are related to l=0 and l=1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature was derived to be 8600$pm$200 K, log g is 4.1$pm$0.2, and the projected rotational velocity is 53$pm$1km/s. Using our Teff value and the radius of 1.8$pm$0.5 Rsun derived from SED fitting, we get a log L/Lsun of 1.20$pm$0.14 which agrees well to the seismologically determined values of 1.65 Rsun and, hence, a log L/Lsun of 1.13. The radial velocity of 14$pm$2 km/s we derived for HD 261711, confirms the stars membership to NGC 2264. Our asteroseismic models suggest that HD 261711 is a delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9Msun. HD 261711 is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning.
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