On the age of the Milky Way bulge stellar population

Die Milchstraße unterscheidet sich nicht wesentlich von anderen weit entfernten Spiralgalaxien. Allerdings erlaubt es uns unsere Lage innerhalb der Milchstraße, ihre Sternpopulationen mit einer Genauigkeit zu studieren, wie sie für extragalaktische Quellen undenkbar wäre. Der "Bulge" der Milchstraße (d.h. die Sternpopulation innerhalb von ~3 kpc vom Galaktischen Zentrum) ist die massereichste der verschiedenen Komponenten der Milchstraße, die sehr alte Sterne beherbergt (>10 Milliarden Jahre). Die Untersuchung der Eigenschaften dieser Sternpopulation kann deshalb Aufschluss geben über die Entstehung und Entwicklung der Milchstraße als ganzes, und von Spiralgalaxien im breiteren Kontext. Bislang herrscht weitgehend Konsens bezüglich der globalen kinematischen, chemischen und strukturellen Eigenschaften der Bulge-Population. Das Alter der Sterne im Bulge, oder besser gesagt die Altersverteilung, ist noch nicht vollständig verstanden. Das Ziel dieser Arbeit ist es, bei den Fragen "Wie alt ist der Bulge?"' und "Gibt es einen räumlichen Altersgradienten im Bulge?" anzusetzen, indem das Alter von Sternen in mehreren verschiedenen Feldern bestimmt wird, die alle innerhalb einer Zone von 300 Quadratgrad um das Zentrum des Bulges liegen. Zum Einsatz kommen Aufnahmen des "VISTA Variables in the Vía Láctea" (VVV) Surveys, in denen durch Fitten der Point Spread Function die genauen Magnituden und Farben von einer halben Milliarde Sterne im Bereich des Bulges extrahiert werden. Die neu erstellten photometrischen Kataloge, die auch dafür genutzt werden, die Extinktion in Richtung des Bulges zu ermitteln, werden der gesamten wissenschaftlichen Gemeinschaft öffentlich zugänglich gemacht. Der Beitrag der vorgelagerten Disk-Population entlang der verschiedenen Blickachsen in Richtung Bulge wird mit Hilfe eines statistischen Verfahrens ermittelt und entfernt, um einen finalen Satz an Sternen zu erhalten, der ausschließlich die Bulge-Population repräsentiert. Das Alter der Sterne in verschiedenen Feldern wird durch den Vergleich der Beobachtungen mit synthetischen Sternpopulationsmodellen bestimmt, welche sorgfältig so konstruiert wurden, dass Beobachtungseffekte berücksichtigt werden (Streuung in der Entfernung, differenzielle Rötung, photometrische Vollständigkeit, photometrische und systematische Unsicherheiten). Die Simulationen zur Generierung der synthetischen Poulationen wurden auf zweierlei Arten durchgeführt: i) ein Modell, das eine spektroskopisch bestimmte Metallizitätsverteilung verwendet, dient als A-priori-Verteilung, so dass das Alter als einzig freier Parameter übrig bleibt; ii) ein genetischer Algorithmus findet aus allen möglichen Kombinationen von Alter und Metallizität die beste Lösung heraus (entsprechend einer uniformen A-priori-Verteilung in Alter und Metallizität). Wir schlussfolgern letztlich, dass der Bulge selbst über seine gesamte Ausdehnung hinweg ($|l| 9.5 Milliarden Jahre), mit einem schwachen Altersgradienten von 0.16 Milliarden Jahren pro Grad in Richtung Galaktisches Zentrum.The Milky Way (MW) galaxy is not much different from its faraway cousins. However, our position within the MW allows us to study the properties of its stellar populations with exquisite detail in comparison to extragalactic sources. The bulge of the MW (i.e. the stellar population within ~3 kpc from the Galactic center) is the most massive stellar component of the MW that also hosts very old stars (>10 Gyr), therefore the study of its stellar population properties can shed light on the formation and evolution of the MW as a whole, and of other spiral galaxies at large. So far, there is a general consensus on the global kinematic, chemical and structural properties of the bulge populations, however the age, or rather, the distribution of the ages of the stars in the bulge is yet to be completely understood. In this work we aim at addressing the questions "How old is the bulge?" and "Is there a spatial age gradient in the bulge?" through the determination of the stellar ages in the different fields sparsely distributed within a region of 300 sqr. deg centered on the bulge. We use VISTA Variables in the Vía Láctea (VVV) survey images to extract accurate magnitude and color of half a billion stars in the bulge area using point spread function fitting. The newly derived photometric catalogs, used in addition to probe the extinction towards the bulge, are made publicly available to the entire community. The contribution of the intervening disk population along the bulge lines of sight has been detected and removed by using a statistical approach in order to obtain a final stars sample that is representative of the bulge population only. The determination of the stellar ages in different fields is provided through the comparison between the observations and synthetic stellar population models, which have been carefully tailored to account for the observational effects (i.e. distance dispersion, differential reddening, photometric completeness, photometric and systematic uncertainties). The simulations leading to the construction of synthetic populations have been carried out by using two different methods: i) a model that uses a spectroscopically derived metallicity distribution functions as prior, leaving the age as the only free parameter; ii) a genetic algorithm that finds the best solution within all possible combinations of age and metallicity (i.e. uniform prior in age and metallicity). We ultimately find that the bulge itself appears to be on average old (>9.5 Gyr) throughout its extension (|l| < 10 degr and -10 degr < b < +5 degr), with a mild gradient of about 0.16 Gyr/deg towards the Galactic center

M dwarfs in the b201 tile of the VVV survey: Colour-based Selection, Spectral Types and Light Curves

The intrinsically faint M dwarfs are the most numerous stars in the Galaxy, have main-sequence lifetimes longer than the Hubble time, and host some of the most interesting planetary systems known to date. Their identification and classification throughout the Galaxy is crucial to unravel the processes involved in the formation of planets, stars and the Milky Way. The ESO Public Survey VVV is a deep near-IR survey mapping the Galactic bulge and southern plane. The VVV b201 tile, located in the border of the bulge, was specifically selected for the characterisation of M dwarfs. We used VISTA photometry to identify M dwarfs in the VVV b201 tile, to estimate their subtypes, and to search for transit-like light curves from the first 26 epochs of the survey. UKIDSS photometry from SDSS spectroscopically identified M dwarfs was used to calculate their expected colours in the $YJHK_s$ VISTA system. A colour-based spectral subtype calibration was computed. Possible giants were identified by a $(J-K_s, H_{J})$ reduced proper motion diagram. The light curves of 12.8<$K_s$<15.8 colour-selected M dwarfs were inspected for signals consistent with transiting objects. We identified 23,345 objects in VVV b201 with colours consistent with M dwarfs. We provided their spectral types and photometric distances, up to $\sim$ 300 pc for M9s and $\sim$ 1.2 kpc for M4s, from photometry. In the range 12<$K_s$<16, we identified 753 stars as possible giants out of 9,232 M dwarf candidates. While only the first 26 epochs of VVV were available, and 1 epoch was excluded, we were already able to identify transit-like signals in the light curves of 95 M dwarfs and of 12 possible giants. Thanks to its deeper photometry ($\sim$4 magnitudes deeper than 2MASS), the VVV survey will be a major contributor to the discovery and study of M dwarfs and possible companions towards the center of the Milky Way.Comment: 11 pages, 4 figures. Accepted for publication in Catalogs and data of Astronomy and Astrophysic

On the age of the Milky Way bulge stellar population

Die Milchstraße unterscheidet sich nicht wesentlich von anderen weit entfernten Spiralgalaxien. Allerdings erlaubt es uns unsere Lage innerhalb der Milchstraße, ihre Sternpopulationen mit einer Genauigkeit zu studieren, wie sie für extragalaktische Quellen undenkbar wäre. Der "Bulge" der Milchstraße (d.h. die Sternpopulation innerhalb von ~3 kpc vom Galaktischen Zentrum) ist die massereichste der verschiedenen Komponenten der Milchstraße, die sehr alte Sterne beherbergt (>10 Milliarden Jahre). Die Untersuchung der Eigenschaften dieser Sternpopulation kann deshalb Aufschluss geben über die Entstehung und Entwicklung der Milchstraße als ganzes, und von Spiralgalaxien im breiteren Kontext. Bislang herrscht weitgehend Konsens bezüglich der globalen kinematischen, chemischen und strukturellen Eigenschaften der Bulge-Population. Das Alter der Sterne im Bulge, oder besser gesagt die Altersverteilung, ist noch nicht vollständig verstanden. Das Ziel dieser Arbeit ist es, bei den Fragen "Wie alt ist der Bulge?"' und "Gibt es einen räumlichen Altersgradienten im Bulge?" anzusetzen, indem das Alter von Sternen in mehreren verschiedenen Feldern bestimmt wird, die alle innerhalb einer Zone von 300 Quadratgrad um das Zentrum des Bulges liegen. Zum Einsatz kommen Aufnahmen des "VISTA Variables in the Vía Láctea" (VVV) Surveys, in denen durch Fitten der Point Spread Function die genauen Magnituden und Farben von einer halben Milliarde Sterne im Bereich des Bulges extrahiert werden. Die neu erstellten photometrischen Kataloge, die auch dafür genutzt werden, die Extinktion in Richtung des Bulges zu ermitteln, werden der gesamten wissenschaftlichen Gemeinschaft öffentlich zugänglich gemacht. Der Beitrag der vorgelagerten Disk-Population entlang der verschiedenen Blickachsen in Richtung Bulge wird mit Hilfe eines statistischen Verfahrens ermittelt und entfernt, um einen finalen Satz an Sternen zu erhalten, der ausschließlich die Bulge-Population repräsentiert. Das Alter der Sterne in verschiedenen Feldern wird durch den Vergleich der Beobachtungen mit synthetischen Sternpopulationsmodellen bestimmt, welche sorgfältig so konstruiert wurden, dass Beobachtungseffekte berücksichtigt werden (Streuung in der Entfernung, differenzielle Rötung, photometrische Vollständigkeit, photometrische und systematische Unsicherheiten). Die Simulationen zur Generierung der synthetischen Poulationen wurden auf zweierlei Arten durchgeführt: i) ein Modell, das eine spektroskopisch bestimmte Metallizitätsverteilung verwendet, dient als A-priori-Verteilung, so dass das Alter als einzig freier Parameter übrig bleibt; ii) ein genetischer Algorithmus findet aus allen möglichen Kombinationen von Alter und Metallizität die beste Lösung heraus (entsprechend einer uniformen A-priori-Verteilung in Alter und Metallizität). Wir schlussfolgern letztlich, dass der Bulge selbst über seine gesamte Ausdehnung hinweg ($|l| 9.5 Milliarden Jahre), mit einem schwachen Altersgradienten von 0.16 Milliarden Jahren pro Grad in Richtung Galaktisches Zentrum.The Milky Way (MW) galaxy is not much different from its faraway cousins. However, our position within the MW allows us to study the properties of its stellar populations with exquisite detail in comparison to extragalactic sources. The bulge of the MW (i.e. the stellar population within ~3 kpc from the Galactic center) is the most massive stellar component of the MW that also hosts very old stars (>10 Gyr), therefore the study of its stellar population properties can shed light on the formation and evolution of the MW as a whole, and of other spiral galaxies at large. So far, there is a general consensus on the global kinematic, chemical and structural properties of the bulge populations, however the age, or rather, the distribution of the ages of the stars in the bulge is yet to be completely understood. In this work we aim at addressing the questions "How old is the bulge?" and "Is there a spatial age gradient in the bulge?" through the determination of the stellar ages in the different fields sparsely distributed within a region of 300 sqr. deg centered on the bulge. We use VISTA Variables in the Vía Láctea (VVV) survey images to extract accurate magnitude and color of half a billion stars in the bulge area using point spread function fitting. The newly derived photometric catalogs, used in addition to probe the extinction towards the bulge, are made publicly available to the entire community. The contribution of the intervening disk population along the bulge lines of sight has been detected and removed by using a statistical approach in order to obtain a final stars sample that is representative of the bulge population only. The determination of the stellar ages in different fields is provided through the comparison between the observations and synthetic stellar population models, which have been carefully tailored to account for the observational effects (i.e. distance dispersion, differential reddening, photometric completeness, photometric and systematic uncertainties). The simulations leading to the construction of synthetic populations have been carried out by using two different methods: i) a model that uses a spectroscopically derived metallicity distribution functions as prior, leaving the age as the only free parameter; ii) a genetic algorithm that finds the best solution within all possible combinations of age and metallicity (i.e. uniform prior in age and metallicity). We ultimately find that the bulge itself appears to be on average old (>9.5 Gyr) throughout its extension (|l| < 10 degr and -10 degr < b < +5 degr), with a mild gradient of about 0.16 Gyr/deg towards the Galactic center

The structure behind the Galactic bar traced by red clump stars in the VVV survey★

Red clump stars are commonly used to map the reddening and morphology of the inner regions of the Milky Way. We use the new photometric catalogues of the VISTA Variables in the V´ıa La´ctea survey to achieve twice the spatial resolution of previous reddening maps for Galactic longitudes − 10◦ < l < 10◦ and latitudes −1.5◦ < b < 1.5◦. We use these de- reddened catalogues to construct the Ks luminosity function around the red clump in the Galactic plane. We show that the secondary peak (fainter than the red clump) detected in these regions does not correspond to the bulge red-giant branch bump alone, as previously interpreted. Instead, this fainter clump corresponds largely to the over-density of red clump stars tracing the spiral arm structure behind the Galactic bar. This result suggests that studies aiming to characterize the bulge red-giant branch bump should avoid low galactic latitudes (|b| < 2◦), where the background red clump population contributes significant contamination. It furthermore highlights the need to include this structural component in future modelling of the Galactic bar

Parasitic survey on introduced monk parakeets (Myiopsitta monachus) in Santiago, Chile

Abstract Central Chile has been identified as a unique ecosystem with high conservation priority because of its high levels of endemism and intensive anthropic pressure. Over a period of almost four decades, the monk parakeet has been successful in establishing and dispersing in urban Santiago, although little is known about its potential impact. Furthermore, nothing is known about its epidemiological risks towards animals or even humans. For this reason, we conducted the first parasitic survey of monk parakeets in Chile through capture, necropsy and thorough external and internal inspection of 92 adult individuals. Among these, 45.7% presented lice that were identified as Paragoniocotes fulvofasciatum, 1.1% had mesostigmatid acari and 8.9% had free-ranging acari. Among 89 parakeets, 19.1% had structures identified as Cryptosporidium sp. This study provides the first description of Cryptosporidium sp. in monk parakeets. Along with the presence of a mesostigmatid acarus in one parakeet, this serves as a public health warning, given that both of these parasites have zoonotic potential

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA)

We present CARMA, the Cluster Ages to Reconstruct the Milky Way Assembly project, the aim of which is to determine precise and accurate age measurements for the entire system of known Galactic globular clusters (GCs) and to use them to trace the most significant merger events experienced by the Milky Way. The strength of CARMA relies on the use of homogeneous photometry, theoretical isochrones, and statistical methods, which will enable us to define a systematic uncertainty-free chronological scale for the complete sample of Milky Way GCs. In this paper, we describe the CARMA framework in detail, and present a first application on a sample of six metal-rich GCs, with the aim being to unequivocally elucidate the debated origin of NGC 6388 and NGC 6441. Our results demonstrate that this pair of clusters is coeval with another four systems that have a clear in situ origin. Moreover, their location in the age–metallicity plane matches that occupied by in situ field stars. The accurate age comparison enabled by the CARMA methodology rules out the possibility that NGC 6388 and NGC 6441 were accreted as part of a past merger event