RR Lyrae stars as tracers of substructure and Galactic archaeology

Die eingereichte Arbeit umfasst mehrere Themen, die sich mit der Nutzung von RR-Lyrae-Sternen in verschiedenen astrophysikalischen Anwendungen in Verbindung mit Galaktischer Archäologie be- fassen. Zudem werden Projekte diskutiert, die mit der Pulsation und den physikalischen Eigen- schaften von RR-Lyrae-Veränderlichen in Verbindung stehen. Als Beispiele sind die Unsicherheit der Masse von RR-Lyrae-Sternen und die Verzerrung von photometrischen Lichtkurven aufgrund von Schocks zu nennen. In unserer ersten Studie nutzten wir mehrere Kategorien von veränderlichen Sternen (darunter RR-Lyrae-Veränderliche), um eine kleine Überdichte – genannt SMCNOD – nördlich der Kleinen Mag- ellanschen Wolke zu untersuchen. Mittels veränderlicher Sterne, die räumlich mit SMCNOD assoziiert sind, konnten wir diese Überdichte mit der Kleinen Magellanschen Wolke in Verbindung bringen. Zwei nachfolgende Projekte legten einen Fokus auf die räumliche und kinematische Untersuchung des Galaktischen Bulges mittels RR-Lyrae-Sternen. In der Zentralregion der Milchstraße fanden wir zwei verschiedene Gruppen von RR-Lyrae-Sternen, die sich in ihren Pulsationseigenschaften unterscheiden. Wir assoziierten diese mit den Oosterhoff Gruppen, welche bereits zuvor in der Milchstraße zugehörigen Kugelsternhaufen gefunden wurden. Beide Populationen sind gleichmäßig im Galaktischen Bulge verteilt und keine der beiden kann aus räumlicher und kinematischer Sicht mit dem Galaktischen Balken in Verbindung gebracht werden. Die RR-Lyrae-Sterne in der solaren Umgebung und deren Assoziierung mit der Galaktischen Scheibe wird im folgenden Projekt diskutiert. Wir fanden eine kleine Population von lokalen RR- Lyrae-Sternen (bis zu einer Entfernung von ≈ 3 kpc von der Sonne aus gesehen), die kinematisch und chemisch der Population von Sternen der dünnen Scheibe ähneln. Unsere Entdeckung fordert unser Verständnis der Entstehung der Galaktischen Scheibe heraus, da diese unter der Annahme, dass die RR-Lyrae-Sterne tatsächlich Mitglider der dünnen Galaktischen Scheibe sind, vor mehr als 10 Gyr stattfand. Die letzten beiden Studien befassen sich mit den Eigenschaften von RR-Lyrae-Sternen als verän- derliche Objekte und erweitern unseren derzeitigen Erkenntnisstand bezüglich deren Pulsation und physikalischen Eigenschaften. Als erstes erweiterten wir die derzeitige Anzahl von Kandidaten für Doppelsternsysteme unter den RR-Lyrae-Sternen. Wir analysierten die Variation ihrer Ephimeriden und shätzten die physikalischen Eigenschaften des möglichen Begleiters ab. Des weiteren stellten wir zum ersten Mal eine umfangreiche photometrische Studie der atmosphärischen Schocks in RR- Lyrae-Sternen zur Verfügung. Wir verknüpfen die Ausprägung von Schocks in synchronisierten RR- Lyrae-Lichtkurven mit ihren Pulsationseigenschaften und diskutieren ihr trennscharfes Verhalten im Instabilitätsstreifen

Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters

We present chemodynamical links between the present-day Milky Way halo field star population and Galactic globular clusters (GCs) using a dataset that combines information from the $\rm{\it Gaia}$ space mission and the Sloan Digital Sky Survey (SDSS-IV, DR14). Moreover, we incorporated a sample of halo giant stars with a distinct chemical signature (strong CN bandheads) that resembles the light-elements anomaly otherwise only seen in the second generation of GC stellar populations. Using three different tagging techniques, we could successfully establish unique associations between 151 extratidal stars in the neighborhood of eight GCs. In addition, we traced the possible origin of about $62\%$ of the sample of CN-strong giants to their potential host clusters. Several of the involved GCs have been brought into connection with the Gaia-Enceladus and Sequoia merger events. By establishing kinematic and chemical connections between 17 CN-strong stars and their surrounding fields, we could identify co-moving groups of stars at the same [Fe/H] with a possible cluster origin. We found strong evidence that four CN-strong stars and their associates are connected to the Sagittarius stream whilst their tightly confined [Fe/H] may hint to a birth site in M 54. Finally, we provide tentative estimates for the fraction of first-generation cluster stars among all stars lost to the halo. In the immediate cluster vicinity, this value amounts to $50.0\pm16.7\%$ while the associations in the halo field rather imply $80.2_{-5.2}^{+4.9}\%$. We speculate that -- if proven real by spectroscopic follow-up -- the disparity between these numbers could indicate a major contribution of low-mass clusters to the overall number of stars escaped to the halo or, alternatively, point toward a strong mass loss from the first generation during early cluster dissolution. [abridged]Comment: 20 pages (+9 pages of appendices), 39 figures, 4 tables, accepted for publication in A&

The Milky Way Bulge extra-tidal star survey: BH 261 (AL 3)

The Milky Way Bulge extra-tidal star survey (MWBest) is a spectroscopic survey with the goal of identifying stripped globular cluster stars from inner Galaxy clusters. In this way, an indication of the fraction of metal-poor bulge stars that originated from globular clusters can be determined. We observed and analyzed stars in and around BH 261, an understudied globular cluster in the bulge. From seven giants within the tidal radius of the cluster, we measured an average heliocentric radial velocity of = -61 +- 2.6 km/s with a radial velocity dispersion of \sigma = 6.1 +- 1.9 km/s. The large velocity dispersion may have arisen from tidal heating in the cluster's orbit about the Galactic center, or because BH 261 has a high dynamical mass as well as a high mass-to-light ratio. From spectra of five giants, we measure an average metallicity of = -1.1 +- 0.2 dex. We also spectroscopically confirm an RR Lyrae star in BH 261, which yields a distance to the cluster of 7.1 +- 0.4~kpc. Stars with 3D velocities and metallicities consistent with BH 261 reaching to ~0.5 degrees from the cluster are identified. A handful of these stars are also consistent with the spatial distribution of that potential debris from models focussing on the most recent disruption of the cluster.Comment: accepted for publication in The Astronomical Journa

Petersen diagram revolution

Over the recent years, the Petersen diagram for classical pulsators, Cepheids and RR Lyr stars, populated with a few hundreds of new multiperiodic variables. We review our analyses of the OGLE data, which resulted in a significant extension of the known, and in the discovery of a few new and distinct forms of multiperiodic pulsation. The showcase includes not only radial mode pulsators, but also radial-non-radial pulsators and stars with significant modulation observed on top of the beat pulsation. First theoretical models explaining the new forms of stellar variability are briefly discussed

RR Lyrae Stars Belonging to the Candidate Globular Cluster Patchick 99

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

The Milky Way Bulge Extra-tidal Star Survey: BH 261 (AL 3)

The Milky Way Bulge extra-tidal star survey is a spectroscopic survey with the goal of identifying stripped globular cluster stars from inner Galaxy clusters. In this way, an indication of the fraction of metal-poor bulge stars that originated from globular clusters can be determined. We observed and analyzed stars in and around BH 261, an understudied globular cluster in the bulge. From seven giants within the tidal radius of the cluster, we measured an average heliocentric radial velocity of 〈RV〉 = −61 ± 2.6 km s−1 with a radial velocity dispersion of 〈σ〉 = 6.1 ± 1.9 km s−1. The large velocity dispersion may have arisen from tidal heating in the cluster´s orbit about the Galactic center, or because BH 261 has a high dynamical mass as well as a high mass-to-light ratio. From spectra of five giants, we measure an average metallicity of 〈[Fe/H]〉 = −1.1 ± 0.2 dex. We also spectroscopically confirm an RR Lyrae star in BH 261, which yields a distance to the cluster of 7.1 ± 0.4 kpc. Stars with 3D velocities and metallicities consistent with BH 261 reaching to ∼05 from the cluster are identified. A handful of these stars are also consistent with the spatial distribution of potential debris from models focusing on the most recent disruption of the cluster.Fil: Kunder, Andrea. Saint Martinʼs University; Estados UnidosFil: Prudil, Zdenek. European Southern Observatory Chile.; ChileFil: Covey, Kevin R.. Western Washington University; Estados UnidosFil: Hughes, Joanne. Seattle University; Estados UnidosFil: Joyce, Meridith. Konkoly Observatory; HungríaFil: Simion, Iulia T.. Shanghai Key Lab For Astrophysics; ChinaFil: Rebekah Kuss. Oregon State University; Estados UnidosFil: Campos, Carlos. Saint Martin's University; Estados UnidosFil: Johnson, Christian I.. Space Telescope Science Institute; Estados UnidosFil: Pilachowski, Catherine A.. Indiana University; Estados UnidosFil: Larson, Kristen A.. Western Washington University.; Estados UnidosFil: Koch Hansen, Andreas J.. Astronomisches Rechen-Institut; AlemaniaFil: Marchetti, Tommaso. European Southern Observatory; AlemaniaFil: Rich, Michael R.. University of California at Los Angeles; Estados UnidosFil: Butler, Evan. University of Washington; Estados UnidosFil: Clarkson, William I.. University of Michigan-Dearborn; Estados UnidosFil: Rivet, Michael. Saint Martinʼs University; Estados UnidosFil: Devine, Kathryn. The College of Idaho; Estados UnidosFil: Vivas, A. Katherina. Cerro Tololo Inter-American Observatory; ChileFil: Perren, Gabriel Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Soto, Mario. Instituto de Astronomía y Ciencias Planetarias; ChileFil: Silva, Erika. Western Washington University; Estados Unido