bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hipparcos subdwarfs and globular cluster ages: towards reliable absolute ages
Authors: Pont F. , Mayor M. , Turon C. 
Published: July 2016

The maximum age of galactic globular clusters provides the best observational constraint on the minimum age of the Universe. One of the main “missing link” in the globular cluster age determination has been the lack of a precise calibration, with local subdwarfs, of the position of the subdwarf sequence at different [Fe/H].Hipparcos data may change this situation. As many precise parallaxes become available for local subdwarfs, the distance to globular clusters can be estimated directly from ZAMS fitting to the subdwarf locus. The ages can then be inferred from the turnoff luminosity (a robust prediction of stellar evolution models), rather than using secondary indicators such as Horizontal-Branch position, or indicators depending on the uncertain colour scale such as turnoff colour.Combining Hipparcos parallaxes with [Fe/H] values determined with the CORAVEL spectrometer, we are studying the position of the subdwarfs in the Colour-Magnitude Diagram from a sample of more than 900 subdwarf candidates. Preliminary results are presented here. It is shown that the distances of many subdwarfs had been underestimated in previous studies, mainly because a large fraction of them is in fact evolved off the main sequence into the turnoff or the subgiant branch.
New accuracy levels for solar system ephemerides
Authors: Standish E. M. , Newhall X X 
Published: July 2016

DE403/LE403 is the latest JPL Planetary and Lunar Ephemeris. It represents a number of changes and improvements to previous JPL ephemerides: the reference frame is now that of the IERS, newer and more accurate observations are used in the adjustment process, some of the data reduction techniques have been refined, and improved dynamical modeling has been incorporated into the equations of motion. As a result, the internal accuracy of the inner four planets has been improved. Further, various measurements accurately tie Jupiter onto the IERS Reference Frame. In the future, use of CCD measurements and the Hipparcos Catalogue should improve the ephemerides of the outermost four planets.DE403/LE403 has been integrated over 6000 years, from 3000 BC to 3000 AD. A more condensed representation has been made from this, named DE404/LE404. It replaces DE102 as the new JPL “Long Ephemeris”.
The motion of Pluto over the age of the solar system
Authors: Kinoshita Hiroshi , Nakai Hiroshi 
Published: July 2016

Pluto's motion is chaotic in the sense that the maximum Lyapunov exponent is positive and the Lyapunov time (the inverse of the Lyapunov exponent) is about 20 million years (Myr). We have carried out the numerical integration of Pluto over the age of the solar system (5.7 billion years towards the past and 5.5 billion years towards the future), which is about 280 times of the Lyapunov time. Our integration does not show any indication of gross instability in the motion of Pluto. The time evolution of Keplerian elements of a nearby trajectory of Pluto at first grow linearly with the time and then start to increase exponentially. These exponential divergences stop at about 420 Myr and saturate. The exponential divergences are suppressed by the following three resonances that Pluto has:
(1)Pluto is in the 3:2 mean motion resonance with Neptune and the libration period of the critical argument is about 20000 years.(2)The argument of perihelion librates around 90 degrees and its period is 3.8 Myr.(3)The motion of the Pluto's orbital plane referred to the Neptune's orbital plane is synchronized with the libration of the argument of perihelion (a secondary resonance). The libration period associated with the second resonance is 34.5 Myr.We briefly discuss the motions of Kuiper belt objects in a 3:2 mean motion resonance with Neptune and several possible scenarios how Pluto evolves to the present stable state.
Arops : The ASIAGO Red Objective-Prism Survey
Authors: Munari U. , Passuello R. 
Published: July 2016

AROPS is an objective-prism survey conducted at high galactic latitudes with the 67/92 cm (f=205 cm) Schmidt telescope of the Asiago Astrophysical Observatory (Italy). The basic technical data are:
– TP4415 high resolution plates, 20×20 cm, treated in forming gas (H2+N2) and covering 24 deg2 on sky– 4° UBK7 objective prism, for a dispersion of 1490 Åmm−1 at NaI D– blue side cut-off at 4980 Å using a 2mm GG14 filter, for a recorded λ range 5000–7000 Å– untrailed spectra to record V ∼ 16.5 mag stars with 40 min exposures
Multiwavelength Milky Way: An Educational Poster
Authors: Leisawitz D. , Digel S.W. , Geitz S. 
Published: July 2016

The Astrophysics Data Facility at NASA Goddard Space Flight Center supports the processing, management, and dissemination of data obtained by past, current, and future NASA and international astrophysics missions, and promotes the effective use of those data by the astrophysics community, educators, and the public. Our Multiwavelength Milky Way poster was printed for broad distribution. It depicts the Galaxy at radio, infrared, optical, X-ray, and gamma-ray wavelengths. In particular, the poster contains images of the Galactic 21-cm and CO (J = 1 → 0) line emission, and IRAS 12, 60, and 100 μm, COBE/DIRBE 1.25, 2.2, and 3.5 μm, Digitized Sky Survey optical wavelength, ROSAT/PSPC 0.25, 0.75, and 1.5 keV X-ray, and CGRO/EGRET E > 100 MeV gamma ray broadband emission. All of the data sets are publicly available. Captions describe the Milky Way and what can be learned about the Galaxy from measurements made in each segment of the electromagnetic spectrum. The poster is intended to be an educational tool, one that will stimulate heightened awareness by laypersons of NASA's contribution to modern astronomy.Through an interface available on the World Wide Web at http://adf.gsfc.nasa.gov/adf/adf.html one may view the images that appear on the poster, read the poster captions, and locate the archived data and references.
Cross-Correlation of Large Scale Surveys: Radio-Loud Objects in the Rosat All Sky Survey
Authors: Brinkmann W. , Yuan W. , Siebert J. 
Published: July 2016

There are basically two different approaches to study the physical conditions and the energy transfer processes operating in astronomical objects:
– the detailed observations of a few prominent objects over a wide wavelength range.– the study of the broad band properties of suitably choosen samples
A rotating jet in the quadrupolar Planetary Nebula NGC 6881
Authors: Guerrero M. A. , Manchado A. 
Published: July 2016

There is a renewed interest in the study of the possible precession of the central sources of planetary nebulae. Three different morphological features are considered the effect of precession:
1.Point-symmetric PNe: Objects whose morphological components are symmetrical with respect to reflection through the center.2.Quadrupolar PNe: Characterized by two well-defined pairs of lobes which are symmetric, in pairs, with respect to two different axes. These PNe are very likely the result of two episodic nebular ejection processes, produced at different positions of the symmetry axis.3.Bipolar, rotating episodic jets (or BRET's): Spectacular structures (Lopez, Meaburn, & Palmer 1994) due to the precession of a symmetrical, collimated episodic outflow.
The H–ΩO Diagram from Recent CMB Observations
Authors: Lineweaver C.H. 
Published: July 2016

The CMB is already one of the pillars of the Big Bang model. However it may also become our most powerful tool to distinguish contending models and to determine their cosmological parameters. To realize this goal, more than 20 observational groups and two new satellites are gearing up to make precise measurements of the CMB at small angular scales. In such a situation it is important to keep track of what the CMB data can already say about cosmological parameters.Current CMB data can already be used to constrain cosmological parameters. The results are model dependent. We have obtained contraints on Hubble's constant h and the density of the Universe Ωo in the context of open and critical density CDM models with Λ = 0. In critical density models we obtain h = 0.30+0.18−0.07. This low value is inconsistent with direct measurements of h but fully consistent with four other cosmological measurements: Big Bang nucleosynthesis, cluster baryonic fraction, age constraints from globular clusters and limits on the shape parameter Γ of matter power spectra (in Ωo = 1 models). If Ωo is left as a free parameter the constraints on h are less restrictive: h = 0.40+0.57−0.14. This is fully consistent with local h measurements and the four other cosmological measurements mentioned above. The best-fit density is Ωo = 0.85 and we set an upper limit of Ωo > 0.4 at ∼ 95% CL.At this conference Ostriker has claimed that open-CDM models with Ωo ≈ 0.3 and h ≈ 0.70 are compatible with all current data. However our new CMB data analysis rules this model out at more than ∼ 4σ.
A Probe of Planck Energy Physics
Authors: Occhionero F. , Monastra S. , Baccigalupi C. , Amendo L. 
Published: July 2016

Large scale voids are a very prominent feature in recent redshift surveys: here we attempt an explanation in terms of a first order phase transition occurring during the slow roll epoch of a two field inflation, a process where one field drives the slow roll while the other undergoes quantum tunneling through a potential barrier. The ensuing bubble like perturbations – nucleated at a number of e-folds N ≈ 55 before reheating – are thought to be the precursors of the voids we observe today, while the zero-point fluctuations of the inflaton are the small, Gaussian perturbations seen by COBE on the large angular scales.If this is so, primordial bubbles must have left a trace on the CMB, unless Silk damping and/or early reionization have erased it. We predict this imprint to have power on small angular scales, ≈ 10 arcmin or ≈ ≈ 1000. Therefore the physics at the Planck energy may be tested astronomically both indirectly through the large scale structure and directly through the forthcoming high resolution MAP and Planck satellites.
The Shapes and Shaping of Planetary Nebulae
Authors: Balick Bruce 
Published: July 2016

One of the most striking attributes of planetary nebulae are their complex, yet highly symmetric shapes. The process(es) which shape planetaries are only beginning to be understood. It is proposed that the morphologies of most PNs can be understood within the context of the “interacting winds” wherein a fast but light wind driven by the nucleus rams into an older, slower, and more massive wind, or red giant envelope (“RGE”) ejected earlier.In order to explain the shapes of noncircular PNs, it seems necessary to hypothesize that the slow wind was originally ejected with an enhanced density along an equatorial plane. The morphologies of nearly all PNs can be understood through two basic parameters: the equatorial density contrast in their RGEs, and the degree of interaction between the fast and slow winds.
The Cosmic Distance Scale
Authors: Tammann G.A. 
Published: July 2016

The zero-point of the extragalactic distance scale, defined by about two dozens of nearby, late-type galaxies, has remained nearly unchanged for the last decade, in spite of the advent of new techniques and great efforts. The distances are essentially tied to trigonometric parallax stars and hence independent of the Hyades modulus; they are consistent with RR Lyr stars. The mean zero-point is therefore probably secure to better than 10%.All known secondary distance indicators are still affected by zero-point errors, by problems in the definition of their relation between distance indicator and absolute magnitude (or linear size), and/or by selection bias. The effect of the very important selection bias (Malmquist effect), which causes a seemingly non-linear expansion field, is illustrated by two examples. To test for any true deviations from a linear expansion the Hubble diagram of nearly bias-free first-ranked cluster galaxies and supernovae Ia is shown; this imposes stringent limits on any non-linearity of the Hubble flow within v<5000 km s−1.After freeing the available distances of field galaxies from selection bias and after reducing them to a common zero-point, one finds HO=55–65. Several distance indicators require a best Virgo cluster modulus of (m-M)=31.60, which implies for the Coma cluster (m-M)=35.38 and, with v(Coma)=7217 km s−1, HO=60. Supernovae Ia and first-ranked cluster galaxies out to large distances give HO (global)=53. Thus the evidence from clusters and field galaxies is best satisfied by HO=55; the assigned mean error of ±7 is to indicate a 3σ range of 35<HO<75.Purely physical methods to determine extragalactic distances have modest weight yet; they will contribute eventually much to the determination of HO.If HO were as large as 100, several paradoxa would arise. The Milky Way would have a very high supernova frequency, our Galaxy and M31 would be oversized, the baryon density would fall short to bind clusters, and Friedman universes were excluded.Because all systematic errors have conspired and probably still conspire to measure HO too high, the true value could well be 40. Until new, decisive evidence becomes available, it is suggested for all practical purposes to use HO=50.
Distribution of IRAS Galaxies
Authors: Rowan-Robinson Michael 
Published: July 2016

Infrared wavelengths are free of several of the problems that plague optical galaxy surveys. At high galactic latitude ≥99% of 60μ sources in the IRAS Point Source Catalog, after deletion of obvious stars, are galaxies. At lower latitudes care has to be taken to avoid confusion with emission from interstellar dust (the ‘cirrus’). IRAS galaxies have been used to determined the direction of the gravitational acceleration acting on the Local Group due to galaxies and clusters within about 200 Mpc. This agrees well with the direction of the microwave background dipole. The density of matter in the universe, distributed like IRAS galaxies, needed to account for the observed velocity of the Local Group, corresponds to Ωo = 1.0 ± 0.2. In the standard hot Big Bang model, 90–95% of this matter would have to be non-baryonic.IRAS galaxies are significantly less clustered than optically selected galaxy samples.
The “Gravitational Lens” 3C 321: A Remarkable Impostor
Authors: Filippenko Alexei V. 
Published: July 2016

Recent observations of the radio galaxy 3C 321 are presented. The optical nucleus consists of two components (A, B), separated by ∼ 4″ (∼ 6 kpc), whose low-resolution spectra strongly resemble those of high-ionization type 2 Seyfert nuclei. The relative intensities of the emission lines differ in A and B by less than 1%, and their profiles are almost identical. 3C 321 appears to be a convincing example of a gravitationally lensed object.Careful analysis of high-quality radio and optical data, however, reveals that the system is almost certainly not a lens. The equivalent widths of the emission lines are roughly twice as high in B than in A, and there are significant spatial offsets between regions of bright continuum and line emission. A slight, but fundamental, difference is visible in the two Hα emission profiles. The radial velocities of A and B are discrepant by 31 ± 10 km s−1. Finally, component A is nearly coincident with a flat-spectrum radio core, whereas B is next to an extended, steep-spectrum knot of radio emission.This object should serve as a warning to lens hunters: beware of impostors, whose true properties may be difficult to ascertain without extensive optical and radio observations.
Are LINERs Starbursts or Mini-quasars? A Comparative Study of their Ultraviolet Spectra
Authors: Koratkar Anuradha 
Published: July 2016

Low Ionization Nuclear Emission Line Regions (LINERs) are found in ˜30% of all bright galaxies. The nuclear luminosities in these objects are such that they can be produced by a number of mechanisms and there have been heated debates on the nature of ionizing sources in LINERs. The variety of ionizing mechanisms suggested are low luminosity AGNs, starbursts, shocks, or any combination of these. We have studied Hubble Space Telescope (HST) ultraviolet (UV) spectra of seven LINERs having compact nuclear UV sources.The picture emerging from this comparison is that the compact source observed in these LINER galaxies, at least in some cases, is a nuclear star cluster rather than a low-luminosity active galactic nucleus (AGN). In these cases, the UV luminosity is driven by tens of thousands of O-type stars, depending on the assumed extinction for these objects. The O-stars could be the high-mass end of a bound stellar population, similar to those seen in super star clusters. Our data do not exclude the possibility that a similar stellar continuum source could dominate in all the LINERs. Alternatively, there may be two types of UV-bright LINERs: those where the UV continuum is produced by a starburst, and those where it is nonstellar.The “clearly-stellar”, weak [O I] emitters, LINERs have relatively weak X-ray emission, and their stellar populations probably provide enough ionizing photons to explain the observed optical emission-line flux. The other LINERs, strong [O I] emitters, have severe ionizing photon deficits, for reasonable extrapolations of their UV spectra beyond the Lyman limit, but have an X-ray/UV power ratio that is higher by two orders of magnitudes than that of the “clearly-stellar” LINERs. A component which emits primarily in the extreme-UV may be the main photoionizing agent in these objects.Recent results show that nuclear-starburst and quasar-like activity are often intermingled. Our results extend this result to the lower luminosities of the LINERs.
The Second Byurakan Survey: Faint Markarian Galaxies, AGN and QSOs
Authors: Stepanian J. A. 
Published: July 2016

On the basis of the Second Byurakan Survey (SBS) we have produced the largest and most homogeneous new complete samples of faint Markarian Galaxies and bright QSOs. The volume of reliable investigation of UVX galaxies reaches to ˜ 200 – 250Mpc,– ten times deeper than the FBS.New reliable data for the surface density of bright QSOs in mag. range 16.05 < B < 17.45 and redshift 0.3 < z < 2.2 are presented. The complete sample of bright(B < 17m5) SBS QSOs contains 93 QSOs in these ranges. The new data allow us to assume that bright QSOs fast evolution might be perhaps the result of a selection effect.
Galaxies in Selected Fields of the Second Byurakan Survey
Authors: Hakopian S.A. , Balayan S.K. 
Published: July 2016

The current state of investigation of galaxies in seven fields of the Second Byurakan Sky Survey (SBS) is presented. These fields have been selected by the results of completeness estimation of the samples of galaxies in 65 fields.Observations of the SBS faint candidate galaxies are carried out to complete spectroscopy of galaxies in the selected fields. Currently in one SBS field, with coordinates of center α=15h30m and δ=+59°, the spectra of all galaxies have been obtained and reduced. Besides the redshift and spectral classification, these data allow estimates of the quality of object selection in the Second Byurakan Survey at faint magnitudes.
Supernova Types, Star Formation and AGN
Authors: Turatto Massimo , Cappellaro Enrico , R. Petrosian Artashes 
Published: July 2016

New values of the frequencies of SNe are presented and discussed in relation to their use as SF indicators. The rate of core-collapse SNe is correlated to the colors and the FIR excesses of the parent galaxies in the sense that galaxies with blue colors and strong infrared excess have higher occurrence of type II and Ib/c SNe than other galaxies. This is in agreement with the expectation that they contain a higher fraction of massive stars. Instead no correlation is present for SNIa. The SN frequency does not correlate with the galaxy activity probably because searches are unable to discover SNe in the nuclear regions of galaxies.A number of SNe with spectra similar to those of AGN exist. Their characteristic features are explained with explosion of SNe in dense environments, reminding of cSNR's invoked in the starburst model for AGNs. Some recent, peculiar SNe seem linked to GRB's opening the possibility that at least some GRB's arise from this kind of stellar explosion.
Techniques for Coping with Radio Frequency Interference
Authors: Fisher J. R. 
Published: July 2016

As a complement to spectrum management efforts by radio astronomers a number of observatories and research groups around the world have begun looking into technical solutions to the problem of separating weak cosmic radiation from man-made radio signals. Some of the technical research now getting underway includes: high dynamic range receivers, low-noise superconducting filters, passive digital filtering, adaptive filters, adaptive sidelobe nulling, multi-feed correlation of RFI, and various techniques for signal blanking.Increased technical support to spectrum management can also be provided in the form of accurate and statistically significant characterization of the radio environment, empirical and theoretical improvement of over-the-horizon propagation models, and timely measurements of spurious radiation falling in the protected radio astronomy bands.Finally, credibility of our spectrum management effort can only be maintained by making sure that local radiation under the control of our radio observatories is in compliance with the field strength limits of Recommendation ITU-R R.A.769. This requires sensitive radiation measurements and often shielding of digital equipment, microwave ovens, test equipment, local oscillators, etc.
Chemistry and Depletion in Pre-Stellar Cores
Authors: Rawlings J. M. C. 
Published: July 2016

The star-formation history of molecular cores is largely determined by gas phase chemical processes that are greatly modified by gas-dust interactions. Substantial elemental depletions may result from the efficient formation of refractory grain material. The depletion of carbon and of refractory elements such as S, Si, Mg, etc. in molecular clouds is well known, but is very poorly constrained. Star forming regions are cold, dark and chemically quiescent, so that in addition to the initial elemental depletions, an ongoing dynamical depletion of molecular material occurs as gas-phase material freezes out onto the surface of dust grains. Observational evidence for anomalous depletions in low mass star forming clumps became apparent in the early 1980s when the narrowness of molecular emission lines (especially those of NH3) suggested that high velocity infalling material is being depleted from the gas phase. This prompted further studies into the chemical effects of differential depletion and together with radiative transfer models has established molecular diagnostics of infall/depletion sources. Recent observations at high spatial resolution show direct evidence for gas-phase depletions in the central regions of protostellar cores.In addition to the diagnostic and purely chemical implications for collapsing cores, depletion plays a very active role in the physical evolution of star-forming regions. Most gravitationally unstable low mass cores are believed to be magnetically sub-critical. Recent polarimetric studies of elongated cores are also providing evidence of magnetic alignment, giving strong support to the idea that magnetic fields play a dominant role in core evolution. The relaxation of magnetic pressure (whether through ambipolar diffusion, or by the damping of MHD waves) is critically dependent on the ionization structure which, in turn, is highly sensitive to the elemental and molecular depletions.