Spectroscopic follow-up of the Hercules–Aquila Cloud
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Abstract:
We designed a follow-up program to find the spectroscopic properties of the Hercules-Aquila Cloud (HAC) and test scenarios for its formation. We measured the radial velocities (RVs) of 45 RR Lyrae in the southern portion of the HAC using the facilities at the MDM observatory, producing the first large sample of velocities in the HAC. We found a double-peaked distribution in RVs, skewed slightly to negative velocities. We compared both the morphology of HAC projected onto the plane of the sky and the distribution of velocities in this structure outlined by RR Lyrae and other tracer populations at different distances to N-body simulations. We found that the behaviour is characteristic of an old, well-mixed accretion event with small apo-galactic radius. We cannot yet rule out other formation mechanisms for the HAC. However, if our interpretation is correct, HAC represents just a small portion of a much larger debris structure spread throughout the inner Galaxy whose distinct kinematic structure should be apparent in RV studies along many lines of sight.Keywords:
RR Lyrae variable
Galactic plane
We used the light curve archive of the Qatar Exoplanet Survey (QES) to investigate the RR Lyrae variable stars listed in the General Catalogue of Variable Stars (GCVS). Of 588 variables studied, we reclassify 14 as eclipsing binaries, one as an RS Canum Venaticorum-type variable, one as an irregular variable, four as classical Cepheids, and one as a type II Cepheid, while also improving their periods. We also report new RR Lyrae sub-type classifications for 65 variables and improve on the GCVS period estimates for 135 RR Lyrae variables. There are seven double-mode RR Lyrae stars in the sample for which we measured their fundamental and first overtone periods. Finally, we detect the Blazhko effect in 38 of the RR Lyrae stars for the first time and we successfully measured the Blazhko period for 26 of them.
RR Lyrae variable
Variable star
Instability strip
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We use the pulsational properties of the RR Lyrae variables in the globular cluster NGC 1851 to obtain detailed constraints of the various sub-stellar populations present along its horizontal branch. On the basis of detailed synthetic horizontal branch modeling, we find that minor helium variations (Y ∼ 0.248–0.280) are able to reproduce the observed periods and amplitudes of the RR Lyrae variables, as well as the frequency of fundamental and first-overtone RR Lyrae stars. Comparison of number ratios among the blue and red horizontal branch components and the two observed subgiant branches also suggest that the RR Lyrae variables originated from the progeny of the bright subgiant branch. The RR Lyrae variables with slightly enhanced helium (Y ∼ 0.270–0.280) have longer periods at a given amplitude, as is seen with Oosterhoff II (OoII) RR Lyrae variables, whereas the RR Lyrae variables with Y ∼ 0.248–0.270 have shorter periods, exhibiting properties of Oosterhoff I (OoI) variables. This correlation does suggest that the pulsational properties of RR Lyrae stars can be very useful for tracing the various subpopulations and can provide suitable constraints on the multiple population phenomenon. It appears to be of great interest to explore whether this conclusion can be generalized to other globular clusters hosting multiple populations.
RR Lyrae variable
Horizontal branch
Subgiant
Variable star
Instability strip
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Abstract Having surveyed ≈ 10% of the sky, we have identified more than 130 PN candidates by surveying multicolour Digitized Sky Survey (DSS), Sloan Digitized Sky Survey (SDSS), and combined [O III], Hα and [S II] images. In a first imaging and spectroscopy campaign, 51 objects were identified as true and probable PNe. This work presents an additional 17 probable or possible PNe identified since that study. The majority of these candidates are situated at Galactic latitudes | b | > 5^, with the exception of seven objects located closer to the Galactic plane. Using the techniques described here that do not require any new survey data, we anticipate that many more PNe are waiting to be found, perhaps as many as 90.
Galactic plane
Virtual Observatory
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Abstract We discuss the results of a systematic search for multi-periodic pulsations in Galactic Bulge δ Scuti and RR Lyrae stars. Six “normal” double-mode variables pulsating in two radial modes have been identified (5 δ Scuti-type and 1 RR Lyrae-type). In 37 RR Lyrae stars secondary periodicities very close to the primary pulsation frequency have been detected. These periodicities correspond to nonradial modes of oscillation. They are found in ∼ 23% of RRab and in ∼ 3% of RRc variables of our sample.
RR Lyrae variable
Variable star
Oscillation (cell signaling)
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Paper I: "RR Lyrae Variables in Globular Clusters and the Second-Parameter Phenomenon" Authors: M. Catelan, A. V. Sweigart, J. Borissova Abstract: We propose to use RR Lyrae variables in globular clusters to probe the origin of the second-parameter phenomenon. Paper II: "New Possible Variables in the Outer-Halo Globular Cluster Palomar 3" Authors: J. Borissova, N. Spassova, M. Catelan, V. D. Ivanov Abstract: We present a list of ten possible variable stars in the globular cluster Pal 3. Seven are new suspected variables. The variability of the RR Lyr candidate reported by Burbidge & Sandage (1958), as well as of the Pop. II Cepheid and RR Lyr from Gratton & Ortolani (1984), are confirmed. Paper III: "On the Production of Bright RR Lyrae Variables in Metal-Rich Globular Clusters" Authors: A. V. Sweigart, M. Catelan Abstract: See astro-ph/9708174.
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Phenomenon
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CCD observations have been used to study 16 of the previously known variables in the Oosterhoff type II globular cluster M9. The properties of the RR Lyrae variables in M9 are compared with those in the Oosterhoff type I cluster M3. Methods devised by Simon, Jurcsik, & Kovács have been used to derive physical parameters for the stars from Fourier analysis. The mean metal abundance so derived for M9, [Fe/H] = -1.77, is in good agreement with the metal abundance derived from spectroscopic observations. All methods for calculating the absolute magnitudes of RR Lyrae variables from Fourier coefficients indicate that the RR Lyrae variables in M9 are more luminous than those in M3. However, there are three RR Lyrae stars in M3 that may be as bright as the M9 stars. These three are thought to be in a more advanced evolutionary state than the other M3 RR Lyrae stars. Absolute magnitudes have also been derived for the RR Lyrae stars in M68 and M107. The different methods predict that RR Lyrae stars in metal-poor clusters are more luminous than those in more metal-rich clusters, but there are inconsistencies in the relative luminosities derived by the different methods.
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Variable star
Instability strip
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We present a re-analysis of M33 RR Lyrae variables in four different fields: two inner disc fields and two outer disc fields. These are located at 8.5, 8.7, 36 and 46 arcmin from the centre of M33, respectively. We identify 48 new RR Lyrae variable stars and refine the light-curve properties of 51 previously identified variables. From the light curves, we calculate reddenings and metallicities for each star. Using data in this paper and previously published material, we are able to construct a radial density profile for the RR Lyrae stars in M33. This profile, when plotted in log space, has a slope of ∼−2.0 ± 0.15 which agrees with the radial distribution of halo stars in the Milky Way and M31. This suggests that the majority of M33 RR Lyrae variables observed so far belong to the halo. We also examine the RR Lyrae specific frequency and absolute magnitude relation in M33 and find good agreement with previous studies.
RR Lyrae variable
Local Group
Variable star
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We used the light curve archive of the Qatar Exoplanet Survey (QES) to investigate the RR Lyrae variable stars listed in the General Catalogue of Variable Stars (GCVS). Of 588 variables studied, we reclassify 14 as eclipsing binaries, one as an RS Canum Venaticorum-type variable, one as an irregular variable, four as classical Cepheids, and one as a type II Cepheid, while also improving their periods. We also report new RR Lyrae sub-type classifications for 65 variables and improve on the GCVS period estimates for 135 RR Lyrae variables. There are seven double-mode RR Lyrae stars in the sample for which we measured their fundamental and first overtone periods. Finally, we detect the Blazhko effect in 38 of the RR Lyrae stars for the first time and we successfully measured the Blazhko period for 26 of them.
RR Lyrae variable
Variable star
Instability strip
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Hydrogen emissions of RR Lyrae variables are the imprints of shock waves traveling through their atmospheres. We develop a pattern recognition algorithm, which is then applied to single-epoch spectra of SDSS and LAMOST. These two spectroscopic surveys covered $\sim$ 10,000 photometrically confirmed RR Lyrae stars. We discovered in total 127 RR Lyrae stars with blueshifted Balmer emission feature, including 103 fundamental mode (RRab), 20 first-overtone (RRc), 3 double-mode (RRd), and 1 Blazhko type (temporary classification for RR Lyrae stars with strong Blazhko modulation in Catalina sky survey that cannot be characterized) RR Lyrae variable. This forms the largest database to date of the properties of hydrogen emission in RR Lyrae variables. Based on ZTF DR5, we carried out a detailed light-curve analysis for the Blazhko type RR Lyrae star with hydrogen emission of long-term modulations. We characterize the Blazhko type RR Lyrae star as an RRab and point out a possible Blazhko period. Finally, we set up simulations on mock spectra to test the performance of our algorithm and on the real observational strategy to investigate the occurrence of the "first apparition".
RR Lyrae variable
Balmer series
Variable star
Overtone
LAMOST
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RR Lyrae variable
Distance modulus
Variable star
Apparent magnitude
Absolute magnitude
Blue straggler
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