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Register a new userBlueshifted hydrogen emission and shock wave of RR Lyrae variables in SDSS and LAMOST
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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.
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Steps toward the nature inside RR Lyrae variables can not only improve our understanding of variable stars but also innovate the precision when we use them as tracers to map the structure of the universe. In this work, we develop a hand-crafted one-dimensional pattern recognition pipeline to fetch out the first apparitions, the most prominent observational characteristic of shock. We report the first detection of hydrogen emission lines in the first-overtone and multi-mode RR Lyrae variables. We find that there is an anti-correlation between the intensity and the radial velocity of the emission signal, which is possibly caused by opacity changing in the helium ionization zone. Moreover, we find one RRd star with hydrogen emission that possibly shows Blazhko-type modulations. According to our discoveries, with an enormous volume of upcoming data releases of variable stars and spectra, it may become possible to build up the bridge between shock waves and big problems like the Blazhko effect in non-fundamental mode RR Lyrae stars.
Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated ($O-C$) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 years, leading to a final sample of 12 firm binary candidates. We provide $O-C$ diagrams and binary parameters for this final sample, and also discuss the properties of 8 additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that $gtrsim 4$ per cent of the RRL reside in binary systems.
The history of the observations of RR Lyr variables started in the XIXth century, more than 120 years ago. The very long time baseline of available data combined with the short period of RR Lyrae variables offer an unique opportunity to look at their past as a treasure of valuable information. At this purpose, the amateur/professional association Groupe Europeen dObservations Stellaires (GEOS) has built a database aimed to gather all the published maxima. We could study the period changes due to stellar evolution. Most of the 123 scrutinized RRab stars does not show any significant period variation. This reflects the fact that the rapid evolution is confined in short evolutionary phases. Notwithstanding this, we could put in evidence period increases in 27 stars and decreases in 21 ones. We also used the GEOS database to study the Blazhko effect of galactic RRab stars. The closed curves representing the Blazhko effect are constructed by plotting the magnitudes at maximum vs. the O-C values. We obtained a variegate family of Blazhko potatoes. We could also reconstruct the changes in the pulsational and Blazhko periods of RR Lyr itself, resulted to be completely decoupled. Moreover, the amplitude of the Blazhko effect decreased so much to be hardly detectable by looking at the maxima collected in 2014 only. The effect seems to start again in the 2015 data.
Accurate metallicities of RR Lyrae are extremely important in constraining period-luminosity-metallicity relationships (PLZ), particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope (SALT). We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.13 dex. All but one RR Lyrae in this sample has accurate ({sigma}_parallax ~ 10%) parallax from Gaia. Combining these new high resolution spectroscopic abundances with similar determinations from the literature for 93 stars, we present new PLZ relationships in WISE W1 and W2 magnitudes, and the Wesenheit magnitudes W(W1,V-W1) and W(W2,V-W2).
We present a new complete Near-Infrared (NIR, $JHK_s$) census of RR Lyrae stars (RRLs) in the globular $omega$ Cen (NGC 5139). We collected 15,472 $JHK_s$ images with 4-8m class telescopes over 15 years (2000-2015) covering a sky area around the cluster center of 60x34 arcmin$^2$. These images provided calibrated photometry for 182 out of the 198 cluster RRL candidates with ten to sixty measurements per band. We also provide new homogeneous estimates of the photometric amplitude for 180 ($J$), 176 ($H$) and 174 ($K_s$) RRLs. These data were supplemented with single-epoch $JK_s$ magnitudes from VHS and with single-epoch $H$ magnitudes from 2MASS. Using proprietary optical and NIR data together with new optical light curves (ASAS-SN) we also updated pulsation periods for 59 candidate RRLs. As a whole, we provide $JHK_s$ magnitudes for 90 RRab (fundamentals), 103 RRc (first overtones) and one RRd (mixed--mode pulsator). We found that NIR/optical photometric amplitude ratios increase when moving from first overtone to fundamental and to long-period (P>0.7 days) fundamental RRLs. Using predicted Period-Luminosity-Metallicity relations, we derive a true distance modulus of 13.674$pm$0.008$pm$0.038 mag (statistical error and standard deviation of the median)---based on spectroscopic iron abundances---and of 13.698$pm$0.004$pm$0.048 mag---based on photometric iron abundances. We also found evidence of possible systematics at the 5-10% level in the zero-point of the PLs based on the five calibrating RRLs whose parallaxes had been determined with HST
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