More Like this

1. Metallicities from high-resolution spectra of 49 RR Lyrae variables

   https://doi.org/10.1093/mnras/stab857  

   Gilligan, Christina K; Chaboyer, Brian; Marengo, Massimo; Mullen, Joseph P; Bono, Giuseppe; Braga, Vittorio F; Crestani, Juliana; Dall’Ora, Massimo; Fiorentino, Giuliana; Monelli, Matteo; et al (April 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Accurate metallicities of RR Lyrae are extremely important in constraining period–luminosity–metallicity (PLZ) relationships, particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope. We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.15 dex. All but one RR Lyrae in this sample has accurate ($$\sigma _{\varpi }\lesssim 10{{\ \rm per\ cent}}$$) 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). 

   more » « less
2. Milky Way archaeology using RR Lyrae and type II Cepheids: I. The Orphan stream in 7D using RR Lyrae stars

   https://doi.org/10.1051/0004-6361/202140422  

   Prudil, Z.; Hanke, M.; Lemasle, B.; Crestani, J.; Braga, V. F.; Fabrizio, M.; Koch-Hansen, A. J.; Bono, G.; Grebel, E. K.; Matsunaga, N.; et al (April 2021, Astronomy & Astrophysics)

   null (Ed.)

   We present a chemo-dynamical study of the Orphan stellar stream using a catalog of RR Lyrae pulsating variable stars for which photometric, astrometric, and spectroscopic data are available. Employing low-resolution spectra from the Sloan Digital Sky Survey (SDSS), we determined line-of-sight velocities for individual exposures and derived the systemic velocities of the RR Lyrae stars. In combination with the stars’ spectroscopic metallicities and Gaia EDR3 astrometry, we investigated the northern part of the Orphan stream. In our probabilistic approach, we found 20 single mode RR Lyrae variables likely associated with the Orphan stream based on their positions, proper motions, and distances. The acquired sample permitted us to expand our search to nonvariable stars in the SDSS dataset, utilizing line-of-sight velocities determined by the SDSS. We found 54 additional nonvariable stars linked to the Orphan stream. The metallicity distribution for the identified red giant branch stars and blue horizontal branch stars is, on average, −2.13 ± 0.05 dex and −1.87 ± 0.14 dex, with dispersions of 0.23 and 0.43 dex, respectively. The metallicity distribution of the RR Lyrae variables peaks at −1.80 ± 0.06 dex and a dispersion of 0.25 dex. Using the collected stellar sample, we investigated a possible link between the ultra-faint dwarf galaxy Grus II and the Orphan stream. Based on their kinematics, we found that both the stream RR Lyrae and Grus II are on a prograde orbit with similar orbital properties, although the large uncertainties on the dynamical properties render an unambiguous claim of connection difficult. At the same time, the chemical analysis strongly weakens the connection between both. We argue that Grus II in combination with the Orphan stream would have to exhibit a strong inverse metallicity gradient, which to date has not been detected in any Local Group system. 

   more » « less
3. The Galactic bulge exploration: I. The period–absolute magnitude–metallicity relations for RR Lyrae stars for G _BP , V, G, G _RP , I, J, H , and K _s passbands using Gaia DR3 parallaxes

   https://doi.org/10.1051/0004-6361/202347338  

   Prudil, Z; Kunder, A; Dékány, I; Koch-Hansen, A J (April 2024, Astronomy & Astrophysics)

   We present a new set of period–absolute magnitude–metallicity (PMZ) relations for single-mode RR Lyrae stars calibrated for the opticalG_BP,V,G,G_RP, near-infraredI,J,H, andK_spassbands. We compiled a large dataset (over 100 objects) of fundamental and first-overtone RR Lyrae pulsators consisting of mean intensity magnitudes, reddenings, pulsation properties, iron abundances, and parallaxes measured by theGaiaastrometric satellite in its third data release. Our newly calibrated PMZ relations encapsulate the most up-to-date ingredients in terms of both data and methodology. They are intended to be used in conjunction with large photometric surveys targeting the Galactic bulge, including the Optical Gravitational Lensing Experiment (OGLE), the Vista Variables in the Vía Láctea Survey (VVV), and theGaiacatalog. In addition, our Bayesian probabilistic approach provides accurate uncertainty estimates of the predicted absolute magnitudes of individual RR Lyrae stars. Our derived PMZ relations provide consistent results when compared to benchmark distances to globular clusters NGC 6121 (also known as M 4), NGC 5139 (also known as omega Cen), and Large and Small Magellanic Clouds, which are stellar systems rich in RR Lyrae stars. Lastly, ourK_s-band PMZ relations match well with the previously published PMZ relations based onGaiadata and accurately predict the distance toward the prototype of this class of variables, the eponymic RR Lyr itself. 

   more » « less
4. RR Lyrae Variables as Tracers of the Galactic Bulge Kinematic Structure

   https://doi.org/10.3390/universe8040206  

   Kunder, Andrea M. (April 2022, Universe)

   RR Lyrae stars are recognized as some of the oldest stars in the Universe. In addition, they are some of the few old celestial objects for which distances can be reliably inferred. As such, these stars are excellent tracers of the oldest structures that exist in the inner Galaxy. Although the inner Galaxy is where the oldest structures in the Milky Way are thought to be hidden, it is also a region notoriously difficult to study due to high extinction and crowding. Here, I will summarize how RR Lyrae stars have been used to obtain a more complete picture of the inner Galaxy. In particular, recently, a large sample of RR Lyrae star motions through space have been obtained and compared to younger, more metal-rich stars in the bulge/bar. It is seen that the inner Galaxy RR Lyrae star kinematics are complicated by a mix of a variety of Galactic components. After isolating only those RR Lyrae stars that are confined to the bulge, a subsample of these stars have slower rotation and are less barred than the dominant bar/bulge. Curiously, there is no discernible metallicity [Fe/H] difference between these two subsamples. Old, metal-poor stars in the inner Galaxy need to be properly accounted for when discussing processes that gave rise to the formation of the inner Galaxy and the Galactic bar/bulge. 

   more » « less
5. RR Lyrae Stars Belonging to the Candidate Globular Cluster Patchick 99

   https://doi.org/10.3847/2041-8213/ad20e8  

   Butler, Evan; Kunder, Andrea; Prudil, Zdenek; Covey, Kevin R.; Ball, Macy; Campos, Carlos; Gollnick, Kaylen; Olivares Carvajal, Julio; Hughes, Joanne; Devine, Kathryn; et al (February 2024, The Astrophysical Journal Letters)

   Abstract Patchick 99 is a candidate globular cluster located in the direction of the Galactic bulge, with a proper motion almost identical to the field and extreme field star contamination. A recent analysis suggests it is a low-luminosity globular cluster with a population of RR Lyrae stars. We present new spectra of stars in and around Patchick 99, targeting specifically the three RR Lyrae stars associated with the cluster as well as the other RR Lyrae stars in the field. A sample of 53 giant stars selected from proper motions and a position on the color–magnitude diagram are also observed. The three RR Lyrae stars associated with the cluster have similar radial velocities and distances, and two of the targeted giants also have radial velocities in this velocity regime and [Fe/H] metallicities that are slightly more metal-poor than the field. Therefore, if Patchick 99 is a bona fide globular cluster, it would have a radial velocity of −92 ± 10 km s⁻¹, a distance of 6.7 ± 0.4 kpc (as determined from the RR Lyrae stars), and an orbit that confines it to the inner bulge. 

   more » « less