اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMOST photometry of the RRd Lyrae variable AQ Leo: Two radial modes, 32 combination frequencies, and beyond
51
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Highly precise and nearly uninterrupted optical photometry of the RR Lyrae star AQ Leo was obtained with the MOST (Microvariability & Oscillations of STars) satellite over 34.4 days in February-March 2005. AQ Leo was the first known double-mode RR Lyrae pulsator (RRd star). Three decades after its discovery, MOST observations have revealed that AQ Leo oscillates with at least 42 frequencies, of which 32 are linear combinations (up to the sixth order) of the radial fundamental mode and its first overtone. Evidence for period changes of these modes is found in the data. The other intrinsic frequencies may represent an additional nonradial pulsation mode and its harmonics (plus linear combinations) which warrant theoretical modeling. The unprecedented number of frequencies detected with amplitudes down to millimag precision also presents an opportunity to test nonlinear theories of mode growth and saturation in RR Lyrae pulsators.
قيم البحث
اقرأ أيضاً
We analyse the OGLE-IV photometry of the first overtone and double-mode RR Lyrae stars (RRc/RRd) in the two fields towards the Galactic bulge observed with high cadence. In 27 per cent of RRc stars we find additional non-radial mode, with characteris
tic period ratio, P x /P 1O in (0.6, 0.64). It strongly corroborates the conclusion arising from the analysis of space photometry of RRc stars, that this form of pulsation must be common. In the Petersen diagram the stars form three sequences. In 20 stars we find two or three close secondary modes simultaneously. The additional modes are clearly non-stationary. Their amplitude and/or phase vary in time. As a result, the patterns observed in the frequency spectra of these stars may be very complex. In some stars the additional modes split into doublets, triplets or appear as a more complex bands of increased power. Subharmonics of additional modes are detected in 20 per cent of stars. They also display a complex structure. Including our previous study of the OGLE-III Galactic bulge data, we have discovered 260 RRc and 2 RRd stars with the additional non-radial mode, which is the largest sample of these stars so far. The additional mode is also detected in two Blazhko RRc stars, which shows that the modulation and additional non-radial mode are not exclusive.
Non-radial modes are excited in classical pulsators, both in Cepheids and in RR Lyrae stars. Firm evidence come from the first overtone pulsators, in which additional shorter period mode is detected with characteristic period ratio falling in between
0.60 and 0.65. In the case of first overtone Cepheids three separate sequences populated by nearly 200 stars are formed in the Petersen diagram, i.e. the diagram of period ratio versus longer period. In the case of first overtone RR Lyrae stars (RRc stars) situation is less clear. A dozen or so such stars are known which form a clump in the Petersen diagram without any obvious structure. Interestingly, all first overtone RR Lyrae stars for which precise space-borne photometry is available show the additional mode, which suggests that its excitation is common. Motivated by these results we searched for non-radial modes in the OGLE-III photometry of RRc stars from the Galactic bulge. We report the discovery of 147 stars, members of a new group of double-mode, radial-non-radial mode pulsators. They form a clear and tight sequence in the Petersen diagram, with period ratios clustering around 0.613 with a signature of possible second sequence with higher period ratio (0.631). The scatter in period ratios of the already known stars is explained as due to population effects. Judging from the results of space observations this still mysterious form of pulsation must be common among RRc stars and with our analysis of the OGLE data we just touch the tip of the iceberg.
We have characterized the pulsation properties of 164 candidate RR Lyrae variables (RRLs) and 55 candidate Anomalous and/or short-period Cepheids in Leo I dwarf spheroidal galaxy. On the basis of its RRLs Leo I is confirmed to be an Oosterhoff-interm
ediate type galaxy, like several other dwarfs. We show that in their pulsation properties, the RRLs representing the oldest stellar population in the galaxy are not significantly different from those of five other nearby, isolated dwarf spheroidal galaxies. A similar result is obtained when comparing them to RR Lyrae stars in recently discovered ultra-faint dwarf galaxies. We are able to compare the period distributions and period-amplitude relations for a statistically significant sample of ab type RR Lyrae stars in dwarf galaxies (~1300stars) with those in the Galactic halo field (~14,000stars) and globular clusters (~1000stars). Field RRLs show a significant change in their period distribution when moving from the inner (dG<14 kpc) to the outer (dG>14kpc) halo regions. This suggests that the halo formed from (at least) two dissimilar progenitors or types of progenitor. Considered together, the RRLs in classical dwarf spheroidal and ultra-faint dwarf galaxies-as observed today-do not appear to follow the well defined pulsation properties shown by those in either the inner or the outer Galactic halo, nor do they have the same properties as RRLs in globular clusters. In particular, the samples of fundamental-mode RRLs in dwarfs seem to lack High Amplitudes and Short Periods (HASP:AV>1.0mag and P <0.48d) when compared with those observed in the Galactic halo field and globular clusters. The observed properties of RRLs do not support the idea that currently existing classical dwarf spheroidal and ultra-faint dwarf galaxies are surviving representative examples of the original building blocks of the Galactic halo.
The Optical Gravitational Lensing Experiment (OGLE) is a great source of top-quality photometry of classical pulsators. Collection of variable stars from the fourth part of the project contains more than 38 000 RR Lyrae stars. These stars pulsate mos
tly in the radial fundamental mode (RRab), in radial first overtone (RRc) or in both modes simultaneously (RRd). Analysis of the OGLE data allowed to detect additional non-radial modes in RRc and in RRd stars. We have found more than 260 double-mode stars with characteristic period ratio of the additional (shorter) period to first overtone period around 0.61, increasing the number of known stars of this type by factor of 10. Stars from the OGLE sample form three nearly parallel sequences in the Petersen diagram. Some stars show more than one non-radial mode simultaneously. These modes belong to different sequences.
I discuss a prospect for mode identification from two-passband photometry of forthcoming BRITE space mission. Examples of photometric diagnostic diagrams are shown for three types of main sequence pulsating variables: $beta$ Cephei, Slowly Pulsating
B-type and $delta$ Scuti stars. I consider also taking into account the radial velocity data from simultaneous spectroscopy, which can be carried out from the ground. With such observations, much better discrimination of the spherical harmonic degree, $ell$, can be accomplished and more constraints on stellar parameters and input physics can be derived.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
