An Infrared Coronagraphic Survey for Substellar Companions

We have used the F160W filter (1.4-1.8 um) and the coronagraph on the Near-InfraRed Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope (HST) to survey 45 single stars with a median age of 0.15 Gyr, an average distance of 30 pc, and an average H-magnitude of 7 mag. For the median age we were capable of detecting a 30 M_Jup companion at separations between 15 and 200 AU. A 5 M_Jup object could have been detected at 30 AU around 36% of our primaries. For several of our targets that were less than 30 Myr old, the lower mass limit was as low as a Jupiter mass, well into the high mass planet region. Results of the entire survey include the proper motion verification of five low-mass stellar companions, two brown dwarfs (HR7329B and TWA5B) and one possible brown dwarf binary (Gl 577B/C).Comment: 11 figures, accepted by A

On the 3 dimensional structure of edge-on disk galaxies

A simple algorithm is employed to deproject the two dimensional images of a pilot sample of 12 high-quality images of edge-on disk galaxies and to study their intrinsic 3 dimensional stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dustlane. This could be explained by the widespread presence of a thick disk component in these galaxies. In addition, the 3 dimensional view allows the study of the vertical distribution of the outer disk, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated disks. This could be regarded as a weakening of the "truncation" with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies.Comment: LaTeX, 25 pages, 10 figures (some low resolution), MNRAS accepted. Version with all figures in full resolution (~6MB) available at http://www.astro.rug.nl/~pohlen/pohlen_3Dedgeon.p

Photometric scaling relations of lenticular and spiral galaxies

Photometric scaling relations are studied for S0 galaxies and compared with those for spirals. New 2D K_s-band multi-component decompositions are presented for 122 early-type disk galaxies. Combining with our previous decompositions, the final sample consists of 175 galaxies. As a comparison sample we use the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS), for which similar decompositions have previously been made by us. Our main results are: (1) Important scaling relations are present, indicating that the formative processes of bulges and disks in S0s are coupled like has been previously found for spirals. (2) We obtain median r_{eff}/h_r = 0.20, 0.15 and 0.10 for S0, S0/a-Sa and Sab-Sc galaxies: these are smaller than predicted by simulation models in which bulges are formed by galaxy mergers. (3) The properties of bulges of S0s are different from the elliptical galaxies, which is manifested in the M_K(bulge) vs r_{eff} relation, in the photometric plane, and to some extent also in the Kormendy relation. The bulges of S0s are similar to bulges of spirals with M_K(bulge) < -20 mag. Some S0s have small bulges, but their properties are not compatible with the idea that they could evolve to dwarfs by galaxy harassment. (4) The relative bulge flux B/T for S0s covers the full range found in the Hubble sequence. (5) The values and relations of the parameters of the disks of the S0 galaxies in NIRS0S are similar to those obtained for spirals in the OSUBSGS. Overall, our results support the view that spiral galaxies with bulges brighter than -20 mag in the K-band can evolve directly into S0s, due to stripping of gas followed by truncated star formation.Comment: Accepted to MNRAS, includes a big figure in electronic form, not included her

The kinematic identification of a thick stellar disc in M31

We present the first characterization of a thick disc component in the Andromeda galaxy (M31) using kinematic data from the DEIMOS multi-object spectrograph instrument on Keck II. Using 21 fields in the South West of the galaxy, we measure the lag of this component with respect to the thin disc, as well as the dispersion, metallicity and scale length of the component. We find an average lag between the two components of =46.0+/-3.9km/s. The velocity dispersion of the thick disc is sigma_{thick}=50.8+/-1.9km/s, greater than the value of dispersion we determine for the thin disc, sigma_{thin}=35.7+/-1.0km/s. The thick disc is more metal poor than the thin disc, with [Fe/H]_{spec}=-1.0+/-0.1 compared to [Fe/H]_{spec}=-0.7+/-0.05 for the thin disc. We measure a radial scale length of the thin and thick discs of h_r=7.3+/-1.0 kpc and h_r=8.0+/-1.2 kpc. From this, we infer scale heights for both discs of 1.1+/-0.2 kpc and 2.8+/-0.6 kpc, both of which are ~2--3 times larger than those observed in the Milky Way. We estimate a mass range for the thick disc component of 2.4x10^{10}Msun< M_{*,thick} <4.1x10^{10}Msun. This value provides a useful constraint on possible formation mechanisms, as any proposed method for forming a thick disc must be able to heat (or deposit) at least this amount of material.Comment: 22 pages, 17 figures. Minor revisions made to text following referee report. Accepted for publication in MNRA

A review of elliptical and disc galaxy structure, and modern scaling laws

A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their models to describe the radial distribution of stars in `nebulae'. This article reviews the progress since then, providing both an historical perspective and a contemporary review of the stellar structure of bulges, discs and elliptical galaxies. The quantification of galaxy nuclei, such as central mass deficits and excess nuclear light, plus the structure of dark matter halos and cD galaxy envelopes, are discussed. Issues pertaining to spiral galaxies including dust, bulge-to-disc ratios, bulgeless galaxies, bars and the identification of pseudobulges are also reviewed. An array of modern scaling relations involving sizes, luminosities, surface brightnesses and stellar concentrations are presented, many of which are shown to be curved. These 'redshift zero' relations not only quantify the behavior and nature of galaxies in the Universe today, but are the modern benchmark for evolutionary studies of galaxies, whether based on observations, N-body-simulations or semi-analytical modelling. For example, it is shown that some of the recently discovered compact elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to appear in "Planets, Stars and Stellar Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references incl. many somewhat forgotten, pioneer papers. Original submission to Springer: 07-June-201

Δυναμική μελέτη μιας περίπτωσης medicane

Η παρούσα διπλωματική εργασία αποσκοπεί στη δυναμική μελέτη μιας περίπτωσης ισχυρής κυκλογένεσης που έλαβε χώρα στη Μεσόγειο, την περίοδο 26-30 Σεπτεμβρίου 2018, και για ορισμένο χρονικό διάστημα παρουσίασε δομή μεσογειακού κυκλώνα με τροπικά χαρακτηριστικά (medicane). Για τη μελέτη του συνοπτικού αλλά και δυναμικού περιβάλλοντος του συγκεκριμένου χαμηλού, χρησιμοποιήθηκαν δορυφορικές εικόνες και δεδομένα ανάλυσης του Ευρωπαϊκού Κέντρου Μεσοπρόθεσμης Πρόγνωσης Καιρού (ECMWF) από την Εθνική Μετεωρολογική Υπηρεσία. Ταχεία βάθυνση της επιφανειακής ύφεσης παρουσιάστηκε κατά το χρονικό διάστημα 27 Σεπτεμβρίου 00UTC –28 Σεπτεμβρίου 06 UTC με εκρηκτικό ρυθμό πτώσης της πίεσης, ενώ το σύστημα απέκτησε μορφή μεσογειακού κυκλώνα με τροπικά χαρακτηριστικά κατά το διάστημα 27 Σεπτεμβρίου 18UTC – 29 Σεπτεμβρίου 00UTC, σύμφωνα με μαθηματικό υπολογισμό που λαμβάνει υπόψη δυναμικά κριτήρια. Τα ανώτερα στρώματα συνέβαλαν δυναμικά στη δημιουργία του επιφανειακού χαμηλού, όπως συμβαίνει σε μια συνηθισμένη κυκλογένεση των μέσων γεωγραφικών πλατών. Στα κατώτερα στρώματα μια προϋπάρχουσα βαροκλινική ζώνη πάνω από τις ακτές της Λιβύης συνδυάστηκε με θετική ανωμαλία της επιφανειακής θερμοκρασίας θάλασσας. Κατά τη διάρκεια που ο κυκλώνας παρουσίασε τροπικά χαρακτηριστικά, οι διαβατικές διεργασίες στα κατώτερα στρώματα, λειτούργησαν σαν κινητήριος δύναμη στην εξέλιξη της επιφανειακής κυκλογένεσης και κυριάρχησαν των αντίστοιχων δυναμικών διεργασιών των ανωτέρων στρωμάτων της τροπόσφαιρας. Στις διαβατικές διεργασίες συγκαταλέγονται οι ροές λανθάνουσας κι αισθητής θερμότητας στην κατώτερη τροπόσφαιρα.In this study, a case of explosive cyclogenesis that took place over the central Mediterranean sea during 26-30 September 2018, and obtained a Tropical-Like Cyclone structure (medicane), is being examined. For this study, satellite images and data-analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF), employing a regular 0.1250.125 latitude – longitude grid of the ERA – Interim dataset, are being used. Data are provided by the Hellenic National Meteorological Service (HNMS). During 27 September 00UTC – 28 September 06UTC explosive deepening took place with central mean sea level pressure of about 998,91hPa. The formation of the Mediterranean cyclone with hurricane-like structure, took place in 27 September 18UTC – 29 September 00UTC, according to mathematic criteria, considering dynamical processes. The cyclogenesis, occurred as a result of upper-level dynamics, as an ordinary case of mid-latitudes areas. Thus, the baroclinic instability of lower-levels over Libya, was combined with a Sea Surface Temperature anomaly. During the medicane activity, diabatic processes of lower levels played a leading role in the cyclone’s evolution, in contrast with upper-troposphere dynamics, that did not contribute. Diabatic processes include surface sensible and latent heat fluxes in lower troposphere