34 research outputs found
Promjenjivi izvori u velikim optičkim pregledima neba
No full textThis thesis studies periodic variability in large optical sky surveys, focusing on long-period variable sources. A primary challenge in studying these objects is accurately determining their periods. The first part of this thesis addresses this by introducing a set of filters to reliably identify periods of sources in the SDSS S82, which were previously classified as non-variable. Five quasars with plausible periodic variability were identified by applying several criteria to the light curves. These criteria included requiring at least 25 data points, matching periods in the SDSS gri filters within 0.1%, and ensuring good agreement with a simple sinusoidal model. Potential aliases were filtered out by requiring distinct periods and calculated uncertainties that were not multiples of one year. Additionally, Kuiper statistics were used to ensure no significant gaps or clustering of points in each phase light curve. In the second part of this thesis, the focus is on one of the previously detected quasars with the shortest period of 278 days. This quasar is analyzed using new observations of MgII lines and archived SDSS spectra, providing three epochs of MgII observations. The key findings include the discovery that the newly observed MgII line exhibits a double-peaked profile that changes over time. By comparing synthetic magnitudes with photometric data as well as using the PoSKI model, which analyzes emission lines and light curves of candidate supermassive binary black holes (SMBBH), a correlation was found suggesting a closely orbiting SMBBH. The latest release Gaia DR3, included light curves for all objects within a field centered on the Andromeda Galaxy. The final scientific part of this thesis focuses on identifying Mira stars in the M31 galaxy and determining their periods. For the first time, a period-luminosity (PL) relation for Mira variables in the M31 galaxy has been established using Gaia filters. This relation is compared with PL relations for multiple galaxies presented in other works, using 2MASS data. Although the method can be improved, the results are promising and lay the groundwork for future research utilizing Gaia’s light curves for the entire sky.Ova disertacija istražuje dugoperiodičnu promjenjivost u velikim optičkim pregledima neba. Periodički promjenjivi izvori ključni su za procjenu udaljenosti u svemiru. Osim toga, promatranje periodične promjenjivosti u AGN-ovima može pružiti uvid u mogućnost sustava dvojnih crnih rupa, čime se postavlja temelj za proučavanje gravitacijskih valova. Glavni izazov u proučavanju promjenjivih izvora je točno određivanje njihovih perioda. U poglavlju 4 uvedene su metode filtracije za pouzdano određivanje perioda objekata prethodno klasificiranih kao nepromjenjivi. Identificirano je pet kvazara s mogućom periodičkom promjenjivošću u SDSS ugriz filtrima, pri čemu je kvazar s najkraćim periodom odabran za daljnje istraživanje. Buduća istraživanja će imati koristi od nadolazećih osjetljivih pregleda neba, poix Prošireni sažetak put Rubin Observatory Legacy Survey of Space and Time, koji će biti učinkovitiji u otkrivanju periodične promjenjivosti. U poglavlju 5 analiziran je jedan od pet identificiranih kvazara koristeći nove MgII linije i arhivirane SDSS spektre, pružajući tri epohe MgII opažanja. Primjenom PoSKI modela utvrđena je povezanost između opaženog ponašanja i modeliranog sustava, sugerirajući prisutnost SMBBH u bliskoj orbiti. Za potvrdu SMBBH sustava potrebna su opsežna promatranja, uključujući daljnje spektroskopsko praćenje i fotometrijska opažanja. Promatranja radio emisije mogla bi pružiti jedinstvenu dijagnostiku okruženja SMBBH sustava. Gaia satelit započeo je svoja znanstvena opažanja 2014. godine, značajna za proučavanje promjenjivih izvora jer Gaia mapira cijelo nebo. U poglavlju 6 identificirane su Mira zvijezde u M31 galaksiji i određeni su njihovi periodi. Po prvi put uspostavljena je PL relacija za Mire u M31 galaksiji koristeći Gaia filtre. Analiza periodičnosti Mira u M31 može se poboljšati uključivanjem čimbenika poput gibanja zvijezda u Andromedi, boje i svih triju Gaia filtera pri izračunu perioda. Gaia DR4 pružit će podatke o krivuljama sjaja za sve opažene izvore, omogućujući primjenu ove metode na druge galaksije
Promjenjivi izvori u velikim optičkim pregledima neba
No full textThis thesis studies periodic variability in large optical sky surveys, focusing on long-period variable sources. A primary challenge in studying these objects is accurately determining their periods. The first part of this thesis addresses this by introducing a set of filters to reliably identify periods of sources in the SDSS S82, which were previously classified as non-variable. Five quasars with plausible periodic variability were identified by applying several criteria to the light curves. These criteria included requiring at least 25 data points, matching periods in the SDSS gri filters within 0.1%, and ensuring good agreement with a simple sinusoidal model. Potential aliases were filtered out by requiring distinct periods and calculated uncertainties that were not multiples of one year. Additionally, Kuiper statistics were used to ensure no significant gaps or clustering of points in each phase light curve. In the second part of this thesis, the focus is on one of the previously detected quasars with the shortest period of 278 days. This quasar is analyzed using new observations of MgII lines and archived SDSS spectra, providing three epochs of MgII observations. The key findings include the discovery that the newly observed MgII line exhibits a double-peaked profile that changes over time. By comparing synthetic magnitudes with photometric data as well as using the PoSKI model, which analyzes emission lines and light curves of candidate supermassive binary black holes (SMBBH), a correlation was found suggesting a closely orbiting SMBBH. The latest release Gaia DR3, included light curves for all objects within a field centered on the Andromeda Galaxy. The final scientific part of this thesis focuses on identifying Mira stars in the M31 galaxy and determining their periods. For the first time, a period-luminosity (PL) relation for Mira variables in the M31 galaxy has been established using Gaia filters. This relation is compared with PL relations for multiple galaxies presented in other works, using 2MASS data. Although the method can be improved, the results are promising and lay the groundwork for future research utilizing Gaia’s light curves for the entire sky.Ova disertacija istražuje dugoperiodičnu promjenjivost u velikim optičkim pregledima neba. Periodički promjenjivi izvori ključni su za procjenu udaljenosti u svemiru. Osim toga, promatranje periodične promjenjivosti u AGN-ovima može pružiti uvid u mogućnost sustava dvojnih crnih rupa, čime se postavlja temelj za proučavanje gravitacijskih valova. Glavni izazov u proučavanju promjenjivih izvora je točno određivanje njihovih perioda. U poglavlju 4 uvedene su metode filtracije za pouzdano određivanje perioda objekata prethodno klasificiranih kao nepromjenjivi. Identificirano je pet kvazara s mogućom periodičkom promjenjivošću u SDSS ugriz filtrima, pri čemu je kvazar s najkraćim periodom odabran za daljnje istraživanje. Buduća istraživanja će imati koristi od nadolazećih osjetljivih pregleda neba, poix Prošireni sažetak put Rubin Observatory Legacy Survey of Space and Time, koji će biti učinkovitiji u otkrivanju periodične promjenjivosti. U poglavlju 5 analiziran je jedan od pet identificiranih kvazara koristeći nove MgII linije i arhivirane SDSS spektre, pružajući tri epohe MgII opažanja. Primjenom PoSKI modela utvrđena je povezanost između opaženog ponašanja i modeliranog sustava, sugerirajući prisutnost SMBBH u bliskoj orbiti. Za potvrdu SMBBH sustava potrebna su opsežna promatranja, uključujući daljnje spektroskopsko praćenje i fotometrijska opažanja. Promatranja radio emisije mogla bi pružiti jedinstvenu dijagnostiku okruženja SMBBH sustava. Gaia satelit započeo je svoja znanstvena opažanja 2014. godine, značajna za proučavanje promjenjivih izvora jer Gaia mapira cijelo nebo. U poglavlju 6 identificirane su Mira zvijezde u M31 galaksiji i određeni su njihovi periodi. Po prvi put uspostavljena je PL relacija za Mire u M31 galaksiji koristeći Gaia filtre. Analiza periodičnosti Mira u M31 može se poboljšati uključivanjem čimbenika poput gibanja zvijezda u Andromedi, boje i svih triju Gaia filtera pri izračunu perioda. Gaia DR4 pružit će podatke o krivuljama sjaja za sve opažene izvore, omogućujući primjenu ove metode na druge galaksije
Promjenjivi izvori u velikim optičkim pregledima neba
No full textThis thesis studies periodic variability in large optical sky surveys, focusing on long-period variable sources. A primary challenge in studying these objects is accurately determining their periods. The first part of this thesis addresses this by introducing a set of filters to reliably identify periods of sources in the SDSS S82, which were previously classified as non-variable. Five quasars with plausible periodic variability were identified by applying several criteria to the light curves. These criteria included requiring at least 25 data points, matching periods in the SDSS gri filters within 0.1%, and ensuring good agreement with a simple sinusoidal model. Potential aliases were filtered out by requiring distinct periods and calculated uncertainties that were not multiples of one year. Additionally, Kuiper statistics were used to ensure no significant gaps or clustering of points in each phase light curve. In the second part of this thesis, the focus is on one of the previously detected quasars with the shortest period of 278 days. This quasar is analyzed using new observations of MgII lines and archived SDSS spectra, providing three epochs of MgII observations. The key findings include the discovery that the newly observed MgII line exhibits a double-peaked profile that changes over time. By comparing synthetic magnitudes with photometric data as well as using the PoSKI model, which analyzes emission lines and light curves of candidate supermassive binary black holes (SMBBH), a correlation was found suggesting a closely orbiting SMBBH. The latest release Gaia DR3, included light curves for all objects within a field centered on the Andromeda Galaxy. The final scientific part of this thesis focuses on identifying Mira stars in the M31 galaxy and determining their periods. For the first time, a period-luminosity (PL) relation for Mira variables in the M31 galaxy has been established using Gaia filters. This relation is compared with PL relations for multiple galaxies presented in other works, using 2MASS data. Although the method can be improved, the results are promising and lay the groundwork for future research utilizing Gaia’s light curves for the entire sky.Ova disertacija istražuje dugoperiodičnu promjenjivost u velikim optičkim pregledima neba. Periodički promjenjivi izvori ključni su za procjenu udaljenosti u svemiru. Osim toga, promatranje periodične promjenjivosti u AGN-ovima može pružiti uvid u mogućnost sustava dvojnih crnih rupa, čime se postavlja temelj za proučavanje gravitacijskih valova. Glavni izazov u proučavanju promjenjivih izvora je točno određivanje njihovih perioda. U poglavlju 4 uvedene su metode filtracije za pouzdano određivanje perioda objekata prethodno klasificiranih kao nepromjenjivi. Identificirano je pet kvazara s mogućom periodičkom promjenjivošću u SDSS ugriz filtrima, pri čemu je kvazar s najkraćim periodom odabran za daljnje istraživanje. Buduća istraživanja će imati koristi od nadolazećih osjetljivih pregleda neba, poix Prošireni sažetak put Rubin Observatory Legacy Survey of Space and Time, koji će biti učinkovitiji u otkrivanju periodične promjenjivosti. U poglavlju 5 analiziran je jedan od pet identificiranih kvazara koristeći nove MgII linije i arhivirane SDSS spektre, pružajući tri epohe MgII opažanja. Primjenom PoSKI modela utvrđena je povezanost između opaženog ponašanja i modeliranog sustava, sugerirajući prisutnost SMBBH u bliskoj orbiti. Za potvrdu SMBBH sustava potrebna su opsežna promatranja, uključujući daljnje spektroskopsko praćenje i fotometrijska opažanja. Promatranja radio emisije mogla bi pružiti jedinstvenu dijagnostiku okruženja SMBBH sustava. Gaia satelit započeo je svoja znanstvena opažanja 2014. godine, značajna za proučavanje promjenjivih izvora jer Gaia mapira cijelo nebo. U poglavlju 6 identificirane su Mira zvijezde u M31 galaksiji i određeni su njihovi periodi. Po prvi put uspostavljena je PL relacija za Mire u M31 galaksiji koristeći Gaia filtre. Analiza periodičnosti Mira u M31 može se poboljšati uključivanjem čimbenika poput gibanja zvijezda u Andromedi, boje i svih triju Gaia filtera pri izračunu perioda. Gaia DR4 pružit će podatke o krivuljama sjaja za sve opažene izvore, omogućujući primjenu ove metode na druge galaksije
An analysis of the uncertainty of the parallaxes obtained with the Gaia satellite
No full textHubbleova konstanta (H_0) je mjera trenutnog širenja svemira. Kako bi se odredila vrijednost H_0, potrebno je razviti i koristiti niz metoda određivanja udaljenosti na međuzvjezdanim, međugalaktičkim i kozmološkim skalama. Često korišten skup metoda, čija osnova su metode bazirane na sjaju opažanih astrofizičkih objekata, je "ljestvica udaljenosti". Važnu stepenicu u ljestvici udaljenosti predstavljaju cefeide, periodički promjenjive zvijezde čiji sjaj je povezan s periodom pulsacija. Kako bi se točno odredio luminozitet cefeida i kalibrirala period-luminozitet relacija, potrebno je točno odrediti udaljenosti cefeida. Jedina čisto geometrijska metoda pomoću koje se mogu odrediti udaljenosti zvijezda u Mliječnom putu je metoda paralakse. Paralakse zvijezda (osim Sunca) su vrlo male, manje od 785 kutnih milisekundi, a mjerljive su do reda veličine kutne mikrosekunde. Mjerenja su podložna raznim sistematskim pogreškama. Jedan od izvora pogrešaka mogu biti i promjene sjaja opažanih zvijezda. U ovom diplomskom radu provjerena je pouzdanost paralaksi cefeida određenih Gaia satelitom Europske svemirske agencije (ESA) usporedbom s paralaksama zvijezda konstantnog sjaja u blizini cefeida. S tim ciljem izvršena je potraga za cefeidama u otvorenim skupovima – gravitacijski povezanim skupinama zvijezda relativno malih prostornih dimenzija s obzirom na njihovu udaljenost od Zemlje. Usporedbom paralaksi otvorenih skupova (određenih kao medijan paralakse zvijezda konstantnog sjaja pojedinog skupa) i cefeida ne može se odbaciti hipoteza da su paralakse cefeida i otvorenih skupova jednake. No, u promatranom uzorku je vidljiv trend većih vrijednosti paralaksi otvorenih skupova. U kontekstu određivanja Hubbleove konstante, ovakav rezultat bi dodatno povećao neslaganje među vrijednostima dobivenim izravnim mjerenjem H_0 i vrijednostima predviđenim ΛCDM modelom na temelju mikrovalnog pozadinskog zračenja opaženog Planck satelitom ESA-eHubble constant (H_0) is the present rate of Universe expansion. H_0 estimation methods critically rely upon distance estimation on interstellar, intergalactic, and cosmological scales. A particularly common suite of distance measuring methods is the "distance ladder". Cepheid variable stars are a crucial rung in the distance ladder as they exhibit well-understood periodluminosity relations. However, to determine the luminosity of the cepheids, precise distances to them must be acquired. The only method free of astrophysical assumptions to determine distances to the stars (except to our Sun) is the stellar parallax method. As parallaxes are typically very small: 785 miliarcseconds in case of Proxima Centauri and typically below miliarcsecond for stars in the Milky Way, their estimation can be affected by a number of systematic effects. One of the key effects may be the variability of the observed source. With this in mind, in this work the Cepheid parallax reported by the European Space Agency’s (ESA) Gaia spacecraft is compared to the parallaxes of the stars nearby the said Cepheids. In order to identify the nearby stars, Cepheids that are members of open clusters (gravitationally bound groups of stars) are identified. Then, the reported Cepheid parallax is compared to the median parallax of the constant stars in the corresponding open cluster. Based on the analysis, the hypothesis that the Cepheid parallaxes and the median open cluster parallaxes are the same cannot be rejected. We do note that there exists an offset between the two samples indicating the open cluster parallaxes are larger. In the context of the Hubble constant tension, this result would further increase the discrepancy between the results reported by the methods measuring the local H_0 and the predictions of the H_0 based on the ΛCDM and the ESA’s Planck spacecraft
Calibration of period-luminosity relations of Mira-type variable stars
No full textOvisnost perioda promjene sjaja i luminoziteta periodički pulsirajućih promjenjivih zvijezda poznata je vise od stoljeća. U međuvremenu su period-luminozitet (PL) relacije postale standardni izbor u određivanju galaktičkih i izvangalaktičkih udaljenosti kada određivanje istih nije dostupno izravnim metodama, poput određivanja udaljenosti metodom trigonometrijske paralakse. Glavni cilj ovog rada je odrediti PL relacije promjenjivih zvijezda tipa Mira iz naše galaksije, Mliječnog puta. U početnom dijelu rada izlažem kratki povijesni pregled PL relacija, njihovu teorijsku pozadinu i opisujem prednosti (u kontekstu PL relacija) promjenjivih zvijezda tipa Mira u odnosu na ostale promjenjive zvijezde. Zatim iznosim podatke i metode kojima sam se koristio. Istraživanje je bilo temeljeno na podacima iz ASAS-SN kataloga, uz infracrvene magnitude (J, H i K_S) iz 2MASS kataloga te paralakse, periode i magnitude (G, G_BP i G_RP ) iz Gaia DR3 kataloga. Metoda preciznih paralaksi predstavlja osnovu ovog rada. Ona se oslanja na korištenje samo najkvalitetnijih podataka iz dostupnih kataloga. Odredio sam tri različite PL relacije, temeljene na magnitudi iz bliskog infracrvenog područja (K_S) te Wesenheit indeksima W_JK i W_G, a konačni rezultati provjereni su usporedbom s vrijednostima iz literature. Nadalje, zbog već poznate ovisnosti PL relacija o kemijskom sastavu zvijezda, ispitao sam istu i na galaktičkim mirama. Rezultati ukazuju kako galaktičke mire odabrane ovom metodom prate iste PL relacije kao i mire iz Velikog Magellanovog oblaka, a unutar W_G-log(P) ravnine dolazi do izraženijeg razdvajanja mira bogatih kisikom (O-mire) i mira bogatih ugljikom (C-mire). U zaključku rada diskutiram nedostatke provedene metode. Odbacivanje nepozitivnih paralaksi, filtriranje podataka prema relativnoj pogrešci paralakse i korištenjem veličina koje nelinearno ovise o paralaksi uvrštava predrasude u konačni uzorak. Kao nastavak na rezultate ovoga rada predlažem korištenje metode temeljene na astrometrijskom luminozitetu, koja bi trebala izbjeći sve spomenute nedostatke.The relation between period and stellar luminosity of periodic variable stars has been known for over a century. Meanwhile, period-luminosity (PL) relations have become a standard tool for calculating galactic and extragalactic distances. The main goal of this thesis is to determine PL relations of galactic Mira-type variable stars. In the first half of the article, I have described a brief history of PL relations, theoretical background, and advantages of mira variables, as distance estimators, over other types of long-period variables. Then, I discuss the used data and methods. Research is based on data from the ASAS-SN catalog, supplemented with 2MASS near-infrared magnitudes (J, H, K_S) and parallaxes, periods, and magnitudes (G, G_BP, G_RP ) from the Gaia DR3 archive. The method of precise parallaxes is the foundation of this work. It is based on parallax-over-error filtering and other selection rules. I have determined three different PL relations, the first is based on near-infrared magnitude KS, and the other two on Wesenheit functions W_JK and W_G. I have compared the final results with already determined PL relations for LMC miras. The conclusion is that galactic Mira-type variables selected by this method follow similar PL relations as their LMC counterparts. Moreover, it is known how stars with different chemical compositions follow different PL relations. Hence, the chemical dependence of PL relations is also investigated. Results show more pronounced separation of O-rich and C-rich mira variables in W_G-log(P) plane. Finally, I have discussed shortcomings of used method, such as removing nonpositive parallaxes and filtering data based on parallax-over-error. Also, I have suggested the astrometry-based luminosity method for future improvements
Classification of variable stars using machine learning methods
No full textProučavanje promjenjivih događaja u svemiru koji se događaju na relativno kratkim vremenskim skalama od velikog je interesa za astrofizičare jer se iz njih mogu dobiti mnoge korisne informacije. Isto vrijedi i za promjenjive zvijezde, to jest zvijezde čiji sjaj nije konstantan. Promatranjem takvih zvijezda moguće je odrediti svojstva zvijezda, u nekim slučajevima i jednostavnije nego kod promatranja nepromjenjivih zvijezda, kao i udaljenosti u svemiru. Kako bismo bili sigurni da su dobivene informacije ispravne, važno je pravilno odrediti kojoj vrsti pripada promjenjiva zvijezda. Međutim, ručno određivanje kategorije za svaku od stotina tisuća promjenjivih zvijezda koje se opažaju u pregledima neba veoma je dug i težak proces. Kako bi se isti ubrzao i automatizirao, mogu se koristiti metode strojnog učenja. U ovom radu korištene su metode klasifikacije i grupiranja sadržane u Scikit-Learn paketu u programskom jeziku Python kako bi se kategoriziralo oko 100000 promjenjivih zvijezda opaženih u Catalina pregledu neba. Za klasifikaciju korišten je Support Vector Machine (SVM) algoritam nadziranog strojnog učenja, a za grupiranje Gaussian Mixture Model (GMM) algoritam nenadziranog strojnog učenja. Dobiveni rezultati uspoređeni su s kategorizacijom provedenom u Catalina pregledu neba kako bi se dobio uvid u to koja metoda je preciznija. Rezultati pokazuju da je SVM algoritam bolji izbor za klasifikaciju ovakvog tipa podataka, ali i on pokazuje neka odstupanja od Catalina pregleda neba. Zaključeno je da se metode strojnog učenja mogu koristiti u traženu svrhu, ali potrebno je još proučavanja kako bi se proces optimizirao.Studying variable cosmic events which happen on relatively short time scales is of great interest for astrophysicists because of a plenitude of useful information one can receive from them. The same is true for variable stars, which are stars whose light is not constant. By observing such stars, it is possible to determine properties of stars, in same cases with less difficulty than by observing non-variable stars, and cosmic distances. To assure that the received information is correct, it is of great importance to correctly determine the type of each variable star. However, determining categories of hundreds of thousands of variable stars in sky surveys is a very long and difficult process. In order to accelerate and automatise said process one can use the machine learning methods. In this paper, the methods of classification and clustering contained in the Scikit-Learn package of the Python programming language were used to categorise roughly 100000 variable stars observed in the Catalina Sky Survey. The supervised learning Support Vector Machine (SVM) algorithm was used for classification and the unsupervised learning Gaussian Mixture Model (GMM) algorithm was used for clustering. Obtained results were compared with the categorisation from the Catalina Sky Survey to gain an insight in the precision of each method. The results show that the SVM algorithm is a better choice for classification of this type of data, but it also shows some deviations from the Catalina Sky Survey. It was concluded that the machine learning methods can be used for desired purposes, but further study is needed to optimise the process
Variability and standard candles in the era of new large-scale surveys
No full textThis thesis focuses on four diverse topics, whose common denominator is the variability revealed by the large scale surveys: i) development of a classified variable star catalog with an unprecedented depth, area coverage, variety of classified variable star types and purity of classification, at the time; ii) an analysis of an extreme coronal-line emitter caused by a tidal disruption of a star by a supermassive black hole; iii) calibration of a new stellar distance estimator applicable at galactic and extragalactic scales and iv) development of photometric pipelines used in the follow-up networks for the Gaia satellite
Exploring The Variable Sky With LINEAR. III. Classification Of Periodic Light Curves
No full textWe describe the construction of a highly reliable sample of ∼7000 optically faint periodic variable stars with light curves obtained by the asteroid survey LINEAR across 10,000 deg2 of the northern sky. The majority of these variables have not been cataloged yet. The sample flux limit is severalmagnitudes fainter than most other wide-angle surveys; the photometric errors range from ∼0.03 mag at r = 15 to ∼0.20 mag at r = 18. Light curves include on average 250 data points, collected over about a decade. Using Sloan Digital Sky Survey (SDSS) based photometric recalibration of the LINEAR data for about 25 million objects, we selected ∼200,000 most probable candidate variables with r \u3c 17 and visually confirmed and classified ∼7000 periodic variables using phased light curves. The reliability and uniformity of visual classification across eight human classifiers was calibrated and tested using a catalog of variable stars from the SDSS Stripe 82 region and verified using an unsupervised machine learning approach. The resulting sample of periodic LINEAR variables is dominated by 3900 RR Lyrae stars and 2700 eclipsing binary stars of all subtypes and includes small fractions of relatively rare populations such as asymptotic giant branch stars and SX Phoenicis stars. We discuss the distribution of these mostly uncataloged variables in various diagrams constructed with optical-to-infrared SDSS, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer photometry, and with LINEAR light-curve features. We find that the combination of light-curve features and colors enables classification schemes much more powerful than when colors or light curves are each used separately. An interesting side result is a robust and precise quantitative description of a strong correlation between the light-curve period and color/spectral type for close and contact eclipsing binary stars (β Lyrae and W UMa): as the color-based spectral type varies from K4 to F5, the median period increases from 5.9 hr to 8.8 hr. These large samples of robustly classified variable stars will enable detailed statistical studies of the Galactic structure and physics of binary and other stars and we make these samples publicly available
REVEALING THE NATURE OF EXTREME CORONAL-LINE EMITTER SDSS J095209.56+214313.3
No full textExtreme coronal-line emitter (ECLE) SDSS J095209.56+214313.3, known by its strong, fading, high-ionization lines, has been a long-standing candidate for a tidal disruption event; however, a supernova (SN) origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: (1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and (2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray telescope (XRT) and the ground-based Mercator telescope. The well-sampled, ~10 yr long, unfiltered LINEAR light curve constrains the onset of the flare to a precision of ±5 days and enables us to place a lower limit on the peak optical magnitude. Difference imaging allows us to estimate the location of the flare in proximity of the host galaxy core. Comparison of the GALEX data (early 2006) with the recently acquired Swift UVOT (2015 June) and Mercator observations (2015 April) demonstrates a decrease in the UV flux over a ~10 yr period, confirming that the flare was UV-bright. The long-lived UV-bright emission, detected 1.8 rest-frame years after the start of the flare, strongly disfavors an SN origin. These new data allow us to conclude that the flare was indeed powered by the tidal disruption of a star by a supermassive black hole and that tidal disruption events are in fact capable of powering the enigmatic class of ECLEs
<i>Gaia </i>Data Release 2: Summary of the contents and survey properties
No full text Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system.
Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results.
Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the G BP (330–680 nm) and G RP (630–1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia -CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.</p
