bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolutionary Histories of Dwarf Galaxies in the Local Group
Authors: Grebel Eva K. 
Published: July 2016

The star formation histories of Local Group (LG) dwarf galaxies and more distant potential LG members are reviewed. Problems in defining the spatial extent of the LG and membership are briefly discussed. The morphological types found in the LG are presented, and it is suggested that we see continuous evolution from low-mass dwarf irregulars (dIrrs) to dwarf spheroidal galaxies (dSphs) in the LG.Star formation histories for LG dwarfs and nearby LG candidates are compiled using population boxes. No two dwarfs, irrespective of morphological type, show the same evolutionary history, and all vary widely in ages of their subpopulations and in their enrichment history. The lack of gas in dSphs and certain dwarf ellipticals (dEs) is puzzling, both with respect to their star formation histories and the expected mass loss from red giants, but a new photoionization scenario may reconcile these contradictions. Old populations, often spatially very extended, may be a common property of dwarf galaxies, though their fractions can be very small. Almost all types of dwarf galaxies studied in detail so far show spatial variations in ages and abundances such as radial age/metallicity gradients. The observed star formation histories impose constraints on merger and accretion scenarios.Properties of the Milky Way dwarf spheroidals are compared to the M31 dSphs and discussed in the framework of the ram pressure/tidal stripping scenario. It is demonstrated that the newly discovered LG dwarfs follow the same relationship for central surface brightness, mean metallicity, and absolute magnitude as the other LG dwarfs.
Differential Abundances of B-type Supergiants in M33
Authors: Monteverde M. I. , Herrero A. 
Published: July 2016

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the following study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. Determination of atmospheric parameters is based on analyses of silicon ionisation balance.Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy.We compare our results with the abundances expected from studies of H II regions.
The Star Formation History in Nearby Dwarf Galaxies: the Fossil Record in the Color-Magnitude Diagram
Authors: Aparicio A. 
Published: July 2016

Dwarf galaxies may play a key role in the formation and evolution of bigger systems. This makes knowing how they form and evolve and, in particular, how their star formation histories (SFHs) have proceeded since their birth, a topic of major interest. For nearby galaxies, the color-magnitude diagram (CMD) contains stars formed over all their lifetime. It is hence a fossil record of their SFHs. The analysis with synthetic CMDs provides a powerful tool to retrieve them.In this paper, I discuss the critical issues related to the computation of synthetic CMDs, present a short summary of the currently available results for the SFH extending the full life of galaxies and make a few critical considerations about the powerfulness and draw-backs of the method.
Stellar populations in starburst galaxies
Authors: Joseph Robert D. 
Published: July 2016

Many galaxies emit a dominant fraction of their bolometric luminosity in the infrared. The small mass-luminosity ratios suggest that these infrared luminosities cannot be sustained by a normal stellar population over a Hubble time. The commonly held explanation is that there has been a burst of star formation sufficiently recently that the full spectrum of the initial mass function up to the highest mass stars is contributing to the luminosity. Starburst galaxies therefore provide laboratories for studying the upper end of the initial mass function.After a briefly summarizing studies of the IMF in the solar neighborhood and in nearby ‘normal’ galaxies, I will turn to studies of environments in which there appears to be evidence for a somewhat different IMF,viz., in starburst galaxies. I will discuss infrared spectroscopic diagnostics of a sample of the most luminous starburst galaxies and what this implies for the IMFs in these ‘violent’ star formation events.
Evolution of Merger Remnants with Supermassive Black Holes
Authors: Tinker Jeremy , Ryden Barbara 
Published: July 2016

We present results of numerical simulations of mergers of spiral galaxies using GADGET (Springel, Yoshida, & White 2001). In three of these simulations one of the progenitor galaxies contained a central supermassive black hole (BH), as well as one simulation which did not contain a BH. The merger remnants were evolved to an age of ∼ 13 Gyr to examine the evolution of the shape of each merger remnant. The results of these simulations were compared to observations of elliptical galaxies, which show that older galaxies appear rounder than younger ones (Ryden, Forbes, & Terlevich 2001).We found that the simulations in which the BH mass was fixed throughout the evolution influence the shape of their host galaxies on timescales less than 3 Gyr. These simulations show little trend of shape with age beyond this time. In the simulations in which the BH mass increased linearly over the duration of the simulation, there is a significant evolution of the shape of the remnant throughout its lifetime, comparable to the observational trend.
Evolution of Rotating White Dwarfs in Close Binaries and Diversity of Type Ia Supernovae
Authors: Uenishi Tatsuhiro , Nomoto Ken'ichi , Hachisu Izumi 
Published: July 2016

Type Ia supernovae are very good, but not perfect, standard candles, because their observed brightness shows a little diversity. The origin of this dibersity needs to be understood for the application to cosmology.In close binary systems, a white dwarf must be rotating faster and faster as it gains angular momentum from the accretion disk. Its rapid rotation affects its final mass and strucure just before a supernova expolosion. Brightness of supernovae can be changed if mass of their progenitors have some diversity.
NIR Spectroscopy of IRAS 16115-5044
Authors: Weldrake David T.F. , Wood Peter R. , Van de Steene Griet C. 
Published: July 2016

IRAS 16115-5044 has been identified as a possible post-AGB star on the basis of its position in the IRAS 2-colour diagram (van der Veen et al. 1989). A study by Van de Steene and Pottasch (1993) failed to detect any radio-continuum flux from the object, suggesting it is still in the pre-planetary nebula phase, that is, the central star is not yet hot enough to ionize the circumstellar shell.The central star is bright in the infrared (K=4.9) but faint in the visible which we attribute to an optically thick circumstellar shell (J-K=2.61, van der Veen et al. 1989). Oudmaijer et al. (1995) obtained a K-band spectrum of lRAS 16115-5044 longward of 2.2 microns, and did not detect any discernable features.
Temperature Scale and Iron Abundances of Very Hot Central Stars of Planetary Nebulae
Authors: Werner Klaus , Deetjen Jochen L. , Dreizler Stefan , Rauch Thomas , Kruk Jeff W. 
Published: July 2016

The determination of effective temperatures of very hot central stars (Teff > 70 000 K) by model atmosphere analyses of optical H and He line profiles is afflicted with considerable uncertainty, primarily due to the lack of neutral helium lines. Ionization balances of metals, accessible only with UV lines, allow more precise temperature estimates. The potential of iron lines is pointed out. At the same time iron and other metal abundances, hardly investigated until today, may be derived from UV spectra. We describe recent HST spectroscopy performed for this purpose.A search for iron lines in FUV spectra of the hottest H-deficient central stars (PG1159-type, Teff >100000 K) taken with FUSE was unsuccessful. The derived deficiency is interpreted in terms of iron depletion due to n-capture nucleosynthesis in intershell matter, which is now exposed at the stellar surface as a consequence of a late He shell flash.
Observations of Planetary Nebulae Haloes
Authors: Corradi Romano L.M. 
Published: July 2016

An improved database of ionized haloes around PNe has been built by adding the results of an extensive observational campaign to the data available in the literature. The new observations allowed us to discovered new haloes around CN 1-5, IC 2165, IC 2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, and possibly IC 1747.The global sample consists of 29 AGB haloes, that are believed to still contain information about the mass loss from the AGB progenitor star. Six of these haloes show a highly asymmetrical geometry that is tentatively ascribed to the interaction of the stellar outflow with the ISM.Another 5 PNe show candidate recombination haloes. These are produced by the recombination front that sets up when the stellar luminosity drops in its post-AGB evolution. The resulting, limb-brightened shell resembles a real AGB halo, but is not related to AGB any mass loss event.Double AGB haloes are found in at least 4 PNe.For 11 PNe, deep images are available, but no halo is found to a level of ≲ 10-3 the peak surface brightness of the inner nebula.These observations show us that ionized haloes are a common morphological component of PNe, being found in 70% of elliptical PNe for which adequately deep images exist. Statistical properties of the haloes are briefly discussed. Using the kinematical ages of the haloes and inner nebulae, we conclude that most of the PNe with detected haloes have hydrogen burning central stars.
Oxygen Abundances for the Planetary Nebulae in M32, NGC 185, and NGC 205
Authors: Richer Michael G. , McCall Marshall L. 
Published: July 2016

We present spectroscopy of planetary nebulae in M32, NGC 185, and NGC 205. With these new data, spectra exist for 14 planetary nebulae in M32, for 5 planetary nebulae in NGC 185, and 13 planetary nebulae in NGC 205. From these data, oxygen abundances based upon electron temperatures derived from detections of [O III]λ4363 may be derived for 11 planetary nebulae in M32, 5 in NGC 185, and 7 in NGC 205. The mean oxygen abundances and their dispersions based upon these [O III]λ4363 detections are 8.51 ± 0.20, 8.21 ± 0.27, and 8.20 ± 0.24 in M32, NGC 185, and NGC 205, respectively, in the usual 12 + log(O/H) format.We confirm a previous finding that a significant fraction of the planetary nebulae in M32 have anomalously strong [N II] lines (Stasińska et al. 1998). Seven of the planetary nebulae for which there now exist spectra (half of the total) have I([N II]λ6584)/I(Hβ) > 1.5. These objects are concentrated towards the centre of M32, though less so than the light.When we combine these new oxygen abundances with extant data, we find that the the same physical processes appear to control the chemical evolution of ellipticals, dwarf spheroidals, and the bulges of spirals. In addition, it is clear that dwarf spheroidals incorporated their metal production into stars much more efficiently than dwarf irregulars, casting more doubt upon an evolutionary link between these two types of dwarf galaxies.
Activity and Kinematics of Late M, L, and T Dwarfs
Authors: Liebert James 
Published: July 2016

The kinematics of late M and certainly L dwarfs indicate that they have a mean age of no more than a few Gyr. This result does not rule out a mix of young brown dwarfs and ZAMS stars. Relative Hα emission strengths begin to decline in the late M dwarfs, even though about 100% of the M7-8 dwarfs show the weaker emission. Both the frequency and likely strength of this emission declines with spectral type among the L's and T's. A larger sample of late M and L dwarfs, which may provide more definitive tests of the kinematic and activity properties, is being assembled from our NStars project.Two unusual objects, one an M9.5e and the other a T6e, show persistent Hα emission at least an order of magnitude stronger than their counterparts of similar spectral type. If these are hypothesized to be very young stellar objects (≲10 Myr) like some observed in Rho Oph, Sigma Ori and Taurus – evolutionary models would require them to have very low masses: In particular, for an entity to fade to a late T dwarf temperature and luminosity within 10 Myr, its mass should be no more than several Jupiters. This seems implausible for an isolated object not near any obvious site of recent star formation. However, our attempt to show that the emission might be due to accretion in a binary system was unsuccessful.
Time-series analysis of the O4 supergiant ζ Puppis
Authors: Reid Andy 
Published: July 2016

Preliminary results of a time-series analysis on a sequence of high dispersion, high-signal-to-noise, optical echelle spectra of the O4 supergiant, ζ Puppis (HD 66811), are presented. Lines of Hei λ5876Å, Heii λ5411Å, Niv λ6381Å and Civ λλ5801, 5812Å are analysed; they show variations in line shape and equivalent width, with ‘bumps’ and ‘dips’ seen moving from blue to red within the line profile. The qualitative pattern of variability seen in all these lines is similar.A Fourier technique, incorporating the iterative clean algorithm, was used on the individual wavelength samples. A periodicity of 8.5-hrs was detected in Heii, and strongly suspected in the remaining absorption lines. This periodicity seems to rule out wind variability as the principal origin for the optical line profile variations seen in ζ Puppis.
Long-term periodic variability in UV absorption lines of the Be star γ Cas: on the relation with V/R variations in the Hβ line
Authors: Telting John H. , Kaper Lex 
Published: July 2016

We present a quantitative study of the variability in ultraviolet resonance lines of Nv, Siiv and Civ of the Be star γ Cas, following up on the work of Henrichs et al. (1983). For this purpose we used 133 IUE spectra obtained over a period of eleven years. Variability occurs in the form of discrete absorption components (DACs), which are formed in the fast-outflowing radiatively driven part of the stellar wind. We constructed a template spectrum from spectra containing no or minor extra absorption due to DACs and modelled the isolated DACs in the obtained quotient spectra. Besides the frequently observed narrow components (vt typically ≤ 250 km/s) at high velocity, we found several broad components occurring at low and intermediate wind velocities.We confirm the finding of Doazan et al. (1987) who reported that the number of observed DACs is associated with the cyclic V/R variability of the Balmer-emission lines. This V/R variability most probably originates in the slowly outflowing high-density equatorial disc-like wind of the star (see e.g. Telting et al. 1993 for the case of γ Cas). We show that when V/R≪1 the central optical depth of DACs is significantly lower than when V/R≪1. In our interpretation this is due to a correlation between the column density associated with the DACs and the phase of the V/R cycle.We find that the Hβ observations of Doazan et al. are consistent with a model in which the cyclic V/R variability is due to a global, one-armed oscillation moving through an equatorial disc (Okazaki 1991, Papaloizou et al. 1992, Savonije and Heemskerk 1993). We suggest that the higher column density of DACs in phases of V/R≪1 is the result of the higher density in the region of their origin, namely close to or in the part of the equatorial disc which is rotating towards the observer.
Investigation of the Local Universe by Means of IRAS Galaxies
Authors: Mickaelian A. M. 
Published: July 2016

The Byurakan-IRAS galaxy (BIG) sample is based on optical identifications of IRAS PSC sources (Beichman, C. A. et al., eds. 1988, Infrared Astronomical Satellite (IRAS) Catalogs and Atlases: The Point Source Catalog, NASA RP–1190, Washington, DC). It makes use of the IR colours, DSS images, and the First Byurakan Spectral Survey (Markarian, B. E. et al. 1989, Commun. Special Astrophys. Obs., 62, 5).All IRAS sources in the region +61° < δ < 90° at high galactic latitudes (|b| >15°) in an area of 1487 deg2 have been revealed up to the limit of the IRAS survey. The BIG sample (Mickaelian, A. M. 2000, Afz, 43, 425 and references therein) consists of 1500 galaxies, including 870 that were previously known. A redshift survey for brighter objects is being carried out with the SAO (Russia) 6 m, Byurakan Observatory 2.6 m, and Observatoire de Haute Provence 1.93 m telescopes. Redshifts in the range of 0.009–0.173 have been measured. For fainter objects, including 30 empty fields corresponding to sources with IR colors typical of galaxies, deep imaging is being carried out to reveal faint objects and study their morphologies. These objects are candidate ULIRGs. Many are multiple galaxies and small groups. About half of the galaxies are radio sources, and a number are also X-ray sources. The IR luminosity may be due to normal star formation or triggered by interaction or active galactic nuclei (AGNs). The AGNs and interacting/merging systems among the nearest BIG objects are the most interesting cases: they provide understanding of the properties of activity, starburst, and interaction phenomena and their interrelation, thus allowing a study of the physics and evolution of galaxies in the Local Universe.
The Optical Spectroscopic Properties of Seyfert 1 Galaxies Selected from Ultraluminous Infrared Galaxies
Authors: Xia X. Y. , Zheng X. Z. , Deng Z. G. 
Published: July 2016

The ultraluminous infrared galaxies (ULIRGs) are strong interacting or merging galaxies. Statistical study shows that about ten percent of ULIRGs are QSOs or Seyfert 1 galaxies, and high–resolution HST images suggest that they are likely to be at the post merger stage. We investigate the optical spectroscopic properties for a complete sample of 28 QSOs/Seyfert 1s selected mainly from the IRAS galaxy redshift survey QDOT and 1.2 Jy catalogs. The optical spectra were obtained with the 2.16 m optical telescope of the Beijing Astronomical Observatory between October 1998 and the end of 1999. Statistical results for both continuum and emission lines show the following:1. Most of our sample galaxies are strong or extremely strong FeII emitters with a ratio of FeII/Hβ larger than 2. There also exists an anti-correlation of the ratio of FeII/Hβ with EW(OIII) and FWHM(Hβ).2. We fit the continuum for all sample galaxies. Aside from a few objects which could be fitted well by a power-law model, the continuum for most sample Seyfert 1 galaxies can be fitted well by a blackbody model or by composites of power–law and blackbody models. For Seyfert 1 galaxies which fit a power–law, E(B-V) is small and in the range of optically selected Seyfert 1 galaxies. However, for Seyfert 1 galaxies fitting a blackbody model, the temperature increases as E(B-V) increases. This is strong observational evidence to support the evolutionary scenario from starbursts to optical QSOs/Seyfert 1s.3. We also discuss the possible mechanism for strong FeII emission from the point of view of evolution of mergers to AGNs.
Cosmic Star Formation Rate at z ~ 3 — Metallicity Effect
Authors: Hirashita H. , Inoue A. K. , Kamaya H. 
Published: July 2016

Infrared (IR) emission from Galactic dust is frequently used as an indicator of the star formation rate (SFR). Recently, A. K. Inoue, H. Hirashita, & H. Kamaya derived a formula for conversion from the IR luminosity to the SFR based on a physical model of H II regions (PASJ, 52, 539, 2000). They expressed this as SFR/(M⊙ yr−1) = {1.1 x 10-10(1-η)/(0.4–0.22f+0.6∊)}(LIR/L⊙), where f is the fraction of ionizing photons absorbed by hydrogen, ∊ is the efficiency of dust absorption for non-ionizing photons, η is the cirrus fraction of the observed dust luminosity, and LIR is the observed luminosity of dust emission. Since f depends on the dust-to-gas ratio and the dust-to-gas ratio is related to metallicity, we present the dependence of the formula on metallicity.Our metallicity-dependent conversion formula is applied to the cosmic star formation history. Based on a recent model of the cosmic star formation history and metal enrichment history, we find that the photons from OB stars are not efficiently reprocessed in the IR before z ~ 3 because of a low dust-to-gas ratio. This indicates that the star formation rate estimated from the submillimeter luminosity using an empirical formula is significantly underestimated (by at least a factor of 3).
The FIRST ESA Cornerstone Mission
Authors: Pilbratt Göran L. 
Published: July 2016

The ‘Far InfraRed and Submillimetre Telescope’ (FIRST) is the fourth cornerstone mission in the European Space Agency (ESA) science programme. It will perform imaging photometry and spectroscopy in the far infrared and submillimetre part of the spectrum, covering approximately the 60–670 μm range.The key science objectives emphasize current questions connected to the formation of galaxies and stars, however, having unique capabilities in several ways.FIRST, a facility available to the entire astronomical community, will carry a 3.5 metre diameter passively cooled telescope. The science pay-load complement – two cameras/medium resolution spectrometers (PACS and SPIRE), and a very high resolution heterodyne spectrometer (HIFI) – will be housed in a superfluid helium cryostat.In early 2007, FIRST will be placed in a transfer trajectory towards its operational orbit around the Earth-Sun L2 point by an Ariane 5 (shared with the ESA cosmic background mapping mission, Planck). Once operational, FIRST will offer a minimum of 3 years of routine observations; roughly 2/3 of the available observing time is open to the general astronomical community through a standard competitive proposal procedure.
The Evolution of QSO Spectra: Evidence for Microlensing?
Authors: Francis Paul J. , Koratkar Anuradha 
Published: July 2016

We find that the spectra of QSOs evolve: high redshift QSOs (z > 1.5) have lower equivalent width emission lines than low redshift QSOs (z < 0.5) with the same luminosities and radio properties.We propose that microlensing by compact objects may account for the apparent evolution. If Ω ∼ 0.05 in compact objects, the continuum emission from many high redshift QSOs will be amplified, but not the line emission, leading to the observed decrease in the apparent equivalent widths.
The ‘Gravitational Lensing’ Bibliography
Authors: Pospieszalska-Surdej A. , Surdej J. , Veron P. 
Published: July 2016

We present a non-exhaustive bibliography on “Gravitational Lensing” (GL), totalizing nearly 1500 titles (see Pospieszalska-Surdej et al. 1993 for an earlier version of this bibliography). It also includes recent abstracts of papers dealing with gravitational lensing and submitted to astro-ph@babbage.sissa.it. The GL bibliography is accessible through a World-Wide-Web page at the URL (cf. next page) http://www.stsci.edu/ftp/stsci/library/grav_lens/grav_lens.html It is also possible to retrieve -via FTP- the latex file ‘grav_bib1.tex’ or the postscript file ‘grav_bib1.ps’ containing the most recent version of this bibliography. Please proceed as follows: ftp stsci.edu, Name: anonymous, Password: your E-mail address, cd stsci/library/grav_lens, get grav_bib1.tex or get grav_bib1.ps, and finally bye).We are aware that the present compilation is not complete, not always uniform and that there are still errors, typos, etc. We would appreciate very much if you could communicate to us (via E-mail: surdej@stsci.edu) missing or new titles (published or accepted for publication), errors, changes and suggestions. It would also be nice for us to receive in the future your preprints or reprints related to ‘Gravitational Lensing’ studies. Please send your material to: A. Pospieszalska-Surdej, STScI, 3700 San Martin Drive, Baltimore MD 21218, USA.