bluuebunny/crossref_metadata_2025 huggingface dataset:
Finding Planets – How do you do it?
Authors: Tinney C. G.
Published: June 2019

Current and future planet search strategies are reviewed.
Masses and Orbits of Extrasolar Planets: Preparation of Astrometric Observing Programs
Authors: Quirrenbach Andreas , Prink Sabine , Mitchell David
Published: June 2019

Astrometry is the most powerful technique to determine dynamical masses and orbital parameters of extrasolar planets. The careful selection and characterization of reference stars is crucial for the success of any astrometric program. The best reference stars for NASA's Space Interferometry Mission (SIM) are distant K giants. The first sub-stellar companion to a K giant was recently detected serendipitously in a radial-velocity survey aimed at defining the SIM grid star strategy.
Radio Emission from Extrasolar Planets
Authors: Farrell W. M. , Lazio T. Joseph W. , Desch M. D. , Bastian T. S. , Zarka P.
Published: June 2019

By virtue of their planetary-scale magnetic fields, the Earth and all of the gas giants in our solar system possess solar-wind deformed magnetospheres. The magnetic polar regions of these “magnetic planets” produce intense, aurora-related radio emission from solar-wind powered electron currents. Simple scaling laws suggest that Jovian-mass planets close to their host stars should produce radio emission; detecting such emission would be the first direct detection of many of these planets. We describe searches using the Very Large Array (VLA) for radio emission from the planets orbiting HD 114762, 70 Vir, and τ Boo. Our limits are just above those predicted for the planetary emissions. We discuss the possibilities for more stringent limits and the implications that the existing observations have for the planets' radio emissions, and hence on the planetary magnetic fields and stellar wind environments.
Preliminary Program for Mars Samples Analysis
Authors: Maurel Marie-Christine , Counil Jean-Louis
Published: June 2019

The main goals of the French Mars exploration program are the development of a netlander for geophysical studies. This project is conducted in the framework of a consortium of European partners (Finland, Germany and Belgium), and an orbiter vehicle of the future Mars sample return mission (MSR) is being developed in cooperation with NASA. Also, we discuss the preparatory program for volatile and rare gas analysis, sample pollution, site selection and Astrobiology.
Ground-based Support of Comet Nuclei Space Missions
Authors: Pittichová Jana , Meech Karen J.
Published: June 2019

There are currently five space missions en route to or planned for comet encounters. It is important for the success of each mission that its target be characterized as fully as possible prior to the encounter. This progress report analyses initial photometric results for 11 comet nuclei for the Stardust, Rosetta, Deep Impact, CONTOUR, Deep Space 1, and the proposed Comet Nucleus Sample Return missions from a database of comet CCD images. Our 17-year database contains more than 20,500 images of ∼160 comets taken during > 1,500 observing hours (Pittichová & Meech 2000). We are undertaking a program to observe these 11 comets over a wide range of heliocentric distances to obtain information about their behavior and composition that will be particularly useful to the space missions.
Comets and the Connection to Life
Authors: Meech K. J. , Bauer J. M.
Published: June 2019

We present a summary of ground-based work being done to gain an understanding of primitive comet, Centaur and Kuiper belt object compositions. We are seeing a diversity of compositions in outer solar system small bodies with respect to the presence of water and organics which may reflect both primordial differences and evolutionary processes.
Comets and the Origin of Life: Structure of Comets Nuclei and Dust
Authors: Levasseur-Regourd A. Chantal , Desvoivres Emmanuel
Published: June 2019

From observations of fragmentation events, clues to a gravitational aggregates structure of some comets nuclei are given. From in-situ and remote light scattering observations, a very high porosity is estimated for dust in comae. These results suggest a possible survival of cometary organics during atmospheric entry at the epoch of intense bombardment. In the coming years, new missions to comets and laboratory measurements on the ISS, will be used to assess such a scenario.
Post-Impact Hydrothermal Activity in Meteorite Impact Craters and Potential Opportunities for Life
Authors: Koeberl Christian , Reimold Wolf Uwe
Published: June 2019

Impact craters are prominent landforms on all objects with a solid surface in the solar system. The formation of an impact structure is a high-energy, high-temperature transient event which introduces large amounts of energy into a limited area. This energy can, in part, be expanded on the creation and activation of a hydrothermal system within and even outside of the crater. Depending on the crater size and geology of the target region, this hydrothermal system may persist for extended periods of time. Such impact-induced hydrothermal systems could well have provided conditions supportive of the development of life on the early Earth and it is not unreasonable to assume that similar conditions could have led to life-favoring circumstances on other planets and satellites.
Constraints on Photosynthesis on Earth and Earth-Like Planets
Authors: Raven John A. , Wolstencroft Ramon D.
Published: June 2019

We discuss how the spectral mismatch between solar radiation at the Earth's surface and the two absorption maxima (440 and 680 nm) of the dominant chlorophyll pigments can be explained as an evolutionary accident of the marine habitat in which photosynthesis evolved on Earth. The geometric rigidity and great stability of chlorophyll make it a likely “universal pigment” given this, together with the spectral absorption properties of water, the evolution of photosynthesis on Earth-like planets (ELPs) orbiting in the habitable zones of A, F and G stars should be relatively straightforward. However for ELPs orbiting cool K and M stars, the effects of variable UV emission from the ELP at earlier epochs and the high absorption of red light by water could lead to a “feast and famine” existence for photosynthetic organisms in the ELP ocean. Pull exploitation of the cool star radiation when UV activity has declined may lead to an evolution of the photosynthetic machinery from the terrestrial two photon to a three photon system.
Feasibility Study for Giant Planet Origins of Life (GPOOLS)
Authors: Troncale Len
Published: June 2019

We recognize the theoretical objections and strong assumptions in bioastronomy against the feasibility of non-carbon based life (NCBL). Yet, we make a long-term commitment to testing these assumptions by parameterization of a wide range of NCBL characteristics using General Morphology, direct lab tests of giant planet gasses and energy sources at extreme temperatures and pressures for spontaneous NCBL subunit formation, and development of a range of instruments for lab and remote sensing of putative NCBL complex macromolecules.
A Scheme for Targeting Optical SETI Observations
Authors: Shostak Seth , Villard Ray
Published: June 2019

In optical SETI (OSETI) experiments, it is generally assumed that signals will be deliberate, narrowly targeted beacons sent by extraterrestrial societies to large numbers of candidate star systems. If this is so, then it may be unrealistic to expect a high duty cycle for the received signal. Ergo, an advantage accrues to any OSETI scheme that realistically suggests where and when to search. In this paper, we elaborate a proposal (Castellano, Doyle, & McIntosh 2000) for selecting regions of sky for intensive optical SETI monitoring based on characteristics of our solar system that would be visible at great distance. This can enormously lessen the amount of sky that needs to be searched. In addition, this is an attractive approach for the transmitting society because it both increases the chances of reception and provides a large reduction in energy required. with good astrometric information, the transmitter need be no more powerful than an automobile tail light.
How to Respond to a SETI Detection
Authors: Norris Ray P.
Published: June 2019

Implicit in the significant resources invested globally in SETI searches is the assumption that there is a small but finite probability that one such search will be successful in the next few years. The potential significance of such an event makes it essential to have contingency plans in place to deal with it. I describe the processes that are in place to deal with a SETI detection, including the SETI Post-Detection Committee and outline the challenges facing us.
Reconstructing the Primordial Power Spectrum
Authors: Bridle S. L. , Lewis A. M. , Weller J. , Efstathiou G.
Published: June 2019

We reconstruct the shape of the primordial power spectrum from the latest cosmic microwave background data, including the new results from the Wilkinson Microwave Anisotropy Probe (WMAP), and large scale structure data from the two degree field galaxy redshift survey (2dFGRS). We discuss two parameterizations taking into account the uncertainties in four cosmological parameters. First we parameterize the initial spectrum by a tilt and a running spectral index, finding marginal evidence for a running spectral index only if the first three WMAP multipoles (ℓ = 2, 3, 4) are included in the analysis. Secondly, to investigate further the low CMB large scale power, we modify the conventional power-law spectrum by introducing a scale above which there is no power. We find a preferred position of the cut at kc ∼ 3 × 10--4 Mpc--1 although kc = 0 (no cut) is not ruled out.
Mapping the Local Structure
Authors: Brent Tully R.
Published: June 2019

A database of 30,000 galaxies within a cube ±8,000 km s--1 centered at our position is used to illustrate the properties of the nearby structure in the distribution of galaxies. The data cube can be manipulated in ways that enhance the visualization of the structure with special software. The dominant regions of high density are the Great Attractor, the Great Wall, and the Perseus-Pisces complexes. There are many voids.
The Relation Between Galactic Properties and Cluster Structure
Authors: Poggianti Bianca M. , Bridges Terry J. , Yagi M. , Kashikawa N. , Komiyama Y. , Okamura S. , Carter Dave , Mobasher Bahram
Published: June 2019

A satisfactory understanding of the origin of the dependence of galaxy properties on their environment has remained, so far, out of reach. In the light of numerous observational results and substantial theoretical progress obtained for clusters of galaxies in the last few years, a primary goal is to understand how the star formation activity depends on cluster substructure, i.e. on the merging/accretion history of a cluster. In this contribution we present a case in which it is possible to identify the cluster environment, and in particular the intracluster medium and the recent infall history of galaxies onto the cluster, as the cause for an abrupt change in the star formation histories of a subset of galaxies in the Coma cluster.
Simulations of the Intergalactic Medium
Authors: Davé Romeel
Published: June 2019

I present an epochal review of baryons in the intergalactic medium (IGM), from the reionization epoch until today. Recent observations indicate a protracted period of reionization, suggesting multiple populations of reionizers; detection of these z ≳ 6 sources is a key goal that is now coming within reach. The optical Lyman alpha forest (2 ≲ z ≲ 4) is well-described by the Fluctuating Gunn-Peterson Approximation, but recent observations of galaxies and metal lines associated with Lyα absorbers remain puzzling. IGM studies at z ≲ 1.5 are progressing rapidly thanks to ultraviolet absorption line studies of both Lyα absorbers and the warm-hot intergalactic medium. Cosmological hydrodynamic simulations have played an integral part in these advances, and have helped to revolutionize our understanding of the IGM at various epochs. Working together, observations and theory continue to expand our knowledge of the IGM as the earliest stage of galaxy formation and the dominant reservoir of baryons at all redshifts.
Damped Lyman-α Absorbers in Cosmological SPH Simulations: the “Metallicity Problem”
Authors: Nagamine Kentaro , Springel Volker , Hernquist Lars
Published: June 2019

We study the distribution of star formation rate (SFR) and metallicity of damped Lyman-α absorbers (DLAs) using cosmological smoothed particle hydrodynamics (SPH) simulations of the Λ cold dark matter (CDM) model. Our simulations include a phenomenological model for feedback by galactic winds which allows us to examine the effect of galactic outflows on the distribution of SFR and metallicity of DLAs. For models with strong galactic winds, we obtain good agreement with recent observations with respect to total neutral hydrogen mass density, NHI column-density distribution, abundance of DLAs, and for the distribution of SFR in DLAs. However, we also find that the median metallicity of simulated DLAs is higher than the values typically observed by nearly an order of magnitude. This discrepancy with observations could be due to shortcomings in the treatment of the supernova feedback or the multiphase structure of the gas in our current simulations. Recent observations by Wolfe et al. (2003a,b) seem to point to the same problem; i.e. the observed DLA metallicities are much lower than those expected from the (either observed or simulated) DLA star formation rates, a puzzle that has been known as the “missing metals”-problem for the globally averaged quantities.
Spectroscopic Observations of Baryons in the Local Universe
Authors: R. Sembach Kenneth
Published: June 2019

There is increasing observational evidence that hot, highly-ionized interstellar and intergalactic gas plays a significant role in the evolution of galaxies in the local universe. Recent observations from several ultraviolet and X-ray observatories have been used to study the highly ionized high velocity cloud system in the vicinity of the Galaxy, the hot gaseous corona of the Galaxy, and highly ionized absorption-line systems at low redshift. The primary spectral diagnostics of this warm-hot interstellar/intergalactic medium are ultraviolet and X-ray absorption lines of O vi and O vii. The observational data fit well into the framework of current theories for the evolution of large-scale structure in the universe, which predict that a significant fraction of the baryonic material at low redshift is contained in highly ionized intergalactic gas. In this paper, I summarize some of the recent highlights of spectroscopic observations of the hot baryons in the local universe.
High-Redshift Galaxies
Authors: Barger Amy
Published: June 2019

Mapping the history of star formation requires combining observations at many wavelengths. The most dramatic episodes of star formation occurred in high-redshift (z > 1) galaxies obscured by dust. These galaxies can be seen at submillimeter wavelengths. While these episodes clearly constitute much of the star formation in the universe, we still do not know the redshift distribution. Although progess has been made in determining the nature of the brightest members of the submillimeter population, these galaxies comprise only a tiny fraction of the submillimeter extragalactic background light. Optical star formation, by contrast, is well mapped but hard to interpret because of the problems of extinction. At recent times there is still substantial star formation, but it primarily takes place in small galaxies. This cosmic downsizing is paralleled by similar evolution in the properties of AGNs.
A Submm View of the Universe: Clues to the Formation of Massive Galaxies
Authors: Smail Ian , Chapman S. C. , Blain A. W. , Ivison R. J.
Published: June 2019

We discuss recent advances in the study of dusty, massive galaxies at z > 1 arising from the first extensive spectroscopic surveys.
Infrared Surveys Planned for ASTRO-F
Authors: Shibai Hiroshi
Published: June 2019

The next survey mission, ASTRO-F, is scheduled for launch in 2005. This is the first Japanese satellite dedicated to infrared astronomy. The primary purpose of this project is to investigate the birth and evolution of galaxies in the early universe through deep, wide-field surveys at wavelengths ranging from 2 to 200 microns. In the far-infrared wavelength band, ASTRO-F will conduct an all-sky survey like the IRAS survey with several tens of times higher sensitivity and several times better spatial resolution. In the near- and mid-infrared, wide area sky-surveys will be conducted over pre-selected portions of the sky in 13 bands ranging from 2-200microns. In addition to these photometric surveys, low-resolution spectroscopic capabilities are available for all wavelength bands. The ASTRO-F mission will produce a fundamental database for the next generation of advanced observatories, for example Herschel, and JWST, and will complement the SIRTF mission by virtue of its wide sky coverage.
Problems with the Current Cosmological Paradigm
Authors: Shanks T.
Published: June 2019

We note that despite the apparent support for the ΛCDM model from the acoustic peaks of the CMB power spectrum and the SNIa Hubble diagram, the standard cosmological model continues to face several fundamental problems. First, the model continues to depend wholly on two pieces of undiscovered physics, namely dark energy and cold dark matter. Then, the implied dark energy density is so small that it is unstable to quantum correction and its size is fine-tuned to the almost impossible level of one part in ≈ 10102; it is also difficult to explain the coincidence between the dark energy, dark matter and baryon densities at the present day. Moreover, any model with a positive Λ also creates fundamental difficulties for superstring theories of quantum gravity. We also review the significant number of astrophysical observations which are now in contradiction with the ΛCDM model. on the grounds that the SNIa Hubble diagram is prone to evolutionary corrections and also that the CMB power spectrum may be contaminated by the effects of foreground ionised gas, we argue that the existence of such systematics could still allow more satisfactory, alternative, models to appear. We suggest that if H0 ≲ 50 kms--1Mpc--1 then a simpler, inflationary model with Ωbaryon = 1 might be allowed with no need for dark energy or cold dark matter. We note that the clear scale error between HST Cepheid and Tully-Fisher galaxy distances and also potential metallicity dependencies for both the Cepheid P-L relation and the SNIa Hubble diagram may mean that such a low value of H0 cannot yet be ruled out.
On the structure and kinematics of molecular clouds from large scale mapping of mm-lines
Authors: Bally J. , Langer W. D. , Wilson R. W. , Stark A. A. , Pound M. W.
Published: June 2019

Molecular gas in the interior of the Orion superbubble consists of sheets, filaments, and partial shells in which the active star forming dense cloud cores are embedded. The main body of the Orion A and B clouds and at least 14 smaller clouds in Orion region are cometary in appearance suggesting strong interaction with massive stars in the Orion OB association. While the small scale (< 1 pc) structure of the clouds may be determined primarily by internal magnetic fields, gravity, and the effects of outflows from young stellar objects, the large scale morphology and kinematics is affected by the energy injected by massive stars. Supernovae, stellar winds, and radiation have compressed, accelerated, ablated, and dispersed molecular gas over the last 107 years. Most GMC/OB star complexes in the Solar neighborhood exhibit morphological and kinematic properties similar to the Orion region. We argue that energy injection by massive stars plays a vital role in the evolution of the ISM and may be responsible for much of the observed large-scale structure and kinematics of molecular clouds.
Observational manifestations of sequential star formation in giant star-gas complexes of the Galaxy
Authors: Sitnik T. G.
Published: June 2019

The age distribution of stars and stellar groupings was studied in the galactic large-scale star-gas complexes (SGCs).
Numerical simulations of turbulent compressible flows
Authors: Pouquet A. , Passot T. , Léorat J.
Published: June 2019

We give an overview of the use of numerical simulations in the modeling of turbulence in molecular clouds.
Signatures of turbulence in the dense interstellar medium
Authors: Falgarone E. , Phillips T.G.
Published: June 2019

We present an ensemble of recent observational results on molecular clouds which, taken separately, could all be understood by invoking various unrelated physical processes, but taken all together form a coherent ensemble stressing the imprints of turbulence in the physics of the cold interstellar medium. These results are first, the existence of wings in the molecular line profiles, which can be interpreted on statistical grounds as the signature of the intermittency of the velocity field in turbulent flows, second the fractal geometry of the cloud edges, with properties reminiscent of those of various surfaces studied in turbulent laboratory flows, and third, the fact that the dense gas fills only a very small fraction of the space. The last points are supported by CO multitransition observations of a few fields in nearby molecular clouds. They show that the excitation conditions are the same for the gas emitting in the linewings and in the linecores and are also remarkably uniform over a large range (factor 10) of column densities. An attractive interpretation of the molecular line data is that most of the 12CO(J=2—1) and (J=3—2) emissions arise in cold (Tk ≥ 10K) and dense (nH2 ∼ 104cm—3 or more) structures distributed on a fractal set with no characteristic scale size greater than about 1000 AU.
On the origin of broad line wings in molecular cloud spectra
Authors: Elmegreen Bruce G.
Published: June 2019

The broad line wings in molecular cloud spectra are proposed to result from strong magnetic waves on the periphery of dense cores and in the intercore regions where the Alfvén velocity should be larger than average. The observed line profiles are reproduced by a simple but realistic model, and the ratio of the broad to the narrow line components is found to equal approximately three, independent of cloud parameters, as long as the core/intercore contrast in the local average density is sufficiently large. Interactions between the magnetic waves should produce dense clumps in the non-linear splash regions between converging flows.
Wave dynamics and star formation in Taurus
Authors: Pudritz Ralph E. , de Castro Ana I. Gomez
Published: June 2019

The mechanism underlying the formation of cores and larger scale structures in molecular clouds must play a fundamental role in the physics of star formation since young stellar objects are usually found within or very near cores (Myers et al 1987, Beichman et al 1986). The Taurus cloud is an ideal object to study in this regard because of its proximity (160 pc), and because only low mass star formation is presently occurring there. Barnard's (1927) beautiful optical photograph of the region reveals that the obscuring gas and dust has filamentary structure that is comparable to the size of the cloud complex (several 10's of pc). This structure is clearly seen in CO maps of the region as well (eg. Duvert et al 1986) where it is apparent that structure on much larger size scales than cores is common. In addition to the filamentary structure one also observes that there are small dark clouds present such as L1489, L1495, etc.
Theoretical and observational aspects of young stars of intermediate mass
Authors: Palla Francesco
Published: June 2019

An account is given of the observational and theoretical properties that characterize young stars of intermediate-mass (2 ≤ M∗ / M⊙ ≤ 10), known as Herbig Ae/Be stars. The mass range of these objects is an interesting one, since it involves the occurrence of complex phenomena associated with the transition from fully convective configurations, typical of T Tauri stars, to radiatively stable objects, as in the case of massive stars. An overview of relevant observations testifying the variety of surface phenomena associated with the Herbig Ae/Be stars is presented. Recent developments in the theory of the formation on intermediate-mass protostars will also be discussed.
A survey of circumstellar structure around young low mass stars
Authors: Terebey S. , Beichman C. A. , Gautier T. N. , Hester J. J. , Myers P. C. , Vogel S. N.
Published: June 2019

We present results from a near-infrared array, CO interferometer, and H2O maser interferometer survey of the circumstellar environments of 26 young low-luminosity embedded stars located in nearby molecular clouds. About 75% of the sample show evidence for stellar winds/outflows in the near-infrared or CO data indicating that most of these sources are in the early wind clearing phase of their evolution. Close to 15% are multiple on the scale of 20″, suggesting that fragmentation of their surrounding dense cloud cores is important before or during gravitational collapse. Roughly 10% have H2O maser emission and the kinematics imply the masers arise in gravitationally unbound gas (i.e., a stellar wind or outflow) rather than in a circumstellar disk.
Aperture synthesis CS and 98 GHz continuum observations of protostellar IRAS sources in Taurus
Authors: Ohashi N. , Kawabe R. , Hayashi M. , Ishiguro M.
Published: June 2019

The CS (J = 2 — 1) line and 98 GHz continuum emission have been observed for 11 protostellar IRAS sources in the Taurus molecular cloud with resolutions of 2.6″−8.8″ (360 AU—1200 AU) using the Nobeyama Millimeter Array (NMA). The CS emission is detected only toward embedded sources, while the continuum emission from dust grains is detected only toward visible T Tauri stars except for one embedded source, L1551-IRS5. This suggests that the dust grains around the embedded sources do not centrally concentrate enough to be detected with our sensitivity (∼4 m Jy r.m.s), while dust grains in disks around the T Tauri stars have enough total mass to be detected with the NMA. The molecular cloud cores around the embedded sources are moderately extended and dense enough to be detected in CS, while gas disks around the T Tauri are not detected because the radius of such gas disks may be smaller than 70 (50 K/Tex) AU. These results imply that the total amount of matter within the NMA beam size must increase when the central objects evolve into T Tauri stars from embedded sources, suggesting that the compact and highly dense disks around T Tauri stars are formed by the dynamical mass accretion during the embedded protostar phase.
Strong magnetic fields in bipolar outflows
Authors: Smith M. D. , Brand P. W. J. L. , Moorhouse A.
Published: June 2019

A supersonic wind from a young star will produce regions of strong magnetic field in the stellar environment. The associated shocks compress the molecular gas, increasing the density n, pressure p, and field B. Crucially, the Alfvén speed, vA∝ B/n1/2, is also increased since the total shock compression is approximately of the form B ∝ n. But is there any evidence for such high vA- or ‘active cloud’ - regions within bipolar outflows? We indicate below one implication which has important observable consequences: fast shocks of low Alfvén number (v/vA) now arise. With a low ionization level, the C-shock structure is qualitatively different from the high Alfvén number flows which are common to ‘quiescent cloud’ conditions. The magnetic-field cushioning now allows molecular hydrogen to survive very fast shocks and broad H2lines are feasible. We display results which show that the resolved broad lines and line ratio properties in the OMC-1 outflow can be explained with fast bow shocks moving through such active regions.
Transfer of continuum UV radiation inside fragmented clouds
Authors: Boisse P.
Published: June 2019

The penetration of visible and UV continuum radiation is a governing factor for many processes inside interstellar clouds. It determines for instance: 1) the overall chemical equilibrium (formation/destruction of molecules and neutral or ionized species, fractional ionization of the gas which is directly related to the coupling with the magnetic field); 2) the overall energy balance (heating of the dust, heating of the gas through collisions with electrons extracted from grains by the photoelectric effect or with grains; 3) cooling of the gas due to fine structure line emission (OI,CI,CII).
Velocity correlations in turbulent molecular clouds
Authors: Deiss B. M. , Just A. , Kegel W. H.
Published: June 2019

The observed widths of molecular lines indicate that molecular clouds are in a highly turbulent state with supersonic internal velocities. At the same time molecular clouds are highly fragmented into substructures exhibiting large density contrasts. These substructures seem to be arranged in a hierarchical order scheme where one can think of newly formed stars representing the smallest spatial scale of ordering. Stars, protostars and even dense clumps can be regarded as being hydrodynamically decoupled from the ambient gas. Thus, in an idealized way, one can think of molecular clouds as being a gravitationally coupled system consisting of gas (continuous component) and ‘point-masses’ (particle component) randomly moving through the gas. The random motion of these ‘point-masses’ is accompanied by spatial and temporal fluctuations of their gravitational potential which, in turn, induce velocity and density fluctuations of the gas.
Processes controlling the initial mass function: interstellar turbulence and magnetic fields
Authors: Fleck R. C.
Published: June 2019

The observed flattening of the initial stellar mass function at low mass can be accounted for in terms of the different interstellar cloud size-mass scaling and different ambipolar diffusion time scaling for small, thermally-supported clouds and larger clouds supported primarily by turbulent pressure.
High resolution infrared maps of IRAS galaxies
Authors: Ghosh S. K. , Rengarajan T. N. , Verma R. P.
Published: June 2019

IRAS has provided infrared maps of a large number of galaxies. However the size of IRAS survey detectors is quite large (∼5′ in the cross-scan direction) and there is a need for improving the resolution of these maps. In order to understand the spatial structure of galaxies, we have generated high resolution maps of 18 large galaxies by deconvolving the IRAS pointed observations from survey detectors as well as from Chopped Photometric Channel (CPC) using Maximum Entropy Method (MEM).
Dense cloud cores
Authors: Güsten R. , Schulz A. , Serabyn E.
Published: June 2019

In order to search for ultra-dense gas condensations as possible sites of future star formation, observations with highest possible angular resolution in high-gas density probing molecular species are required. Here we report first results from two-telescope (IRAM 30-m & CSO 10.4-m) multi-transition excitation studies of the linear molecules CS and HCN, both with critical densities nc∼107 cm−3. We obtained maps towards a number of galactic cloud cores in the CS(J=5−4;7−6) and the HCN(3-2;4-3) mm/submm transitions and those of their optically thin isotopic species (C34S; H13CN) accessible from ground. For a proper excitation analysis, the gas temperature has been determined independently from the symmetric top molecules NH3 or CH3CN. Here we present first results obtained towards the NGC 2024 molecular cloud core (Schulz et al. 1990).
Gravitational instability induced by collisions between non-identical clouds
Authors: Habe Asao , Ohta Kanji
Published: June 2019

In order to investigate gravitational instability induced by supersonic collisions between small, dense clouds and large, diffuse clouds, we perform the numerical hydrodynamic calculation by SPH code. We show that the large cloud is disrupted by the bow shock induced by the small cloud, and the small cloud is compressed. Final fates of the small cloud are divided into two cases. The first case is that the small cloud is ablated by the ram-pressure of the large cloud and is finally destroyed. The second case is that the central part of the small cloud left from the ablation gravitationally collapses. We discuss the condition dividing these two cases. Our condition show that even if the Mach number of collision velocity is very high, the small cloud can collapse.
Magnetic fields in the Solar Nebula and the angular momentum transfer
Authors: Kiguchi M. , Narita S. , Terasawa T. , Hayashi C.
Published: June 2019

We are now carrying out the project to investigate how the primodial solar disk is formed and evolves. One of the central problems of this project is to study the angular momentum transfer in the nebula caused by the magnetic braking or the turbulent mixing in the boundary layer between the surface of the disk and its high temperature corona envelope.
Physical conditions of star forming sites in the S247/252 molecular complex
Authors: Koempe C. , Joncas G. , Wouterloot J.G.A. , Meyerdierks H.
Published: June 2019

By now, it is well established that massive stars form in giant molecular clouds. Numerous studies have shown that star formation, instead of being spread uniformly throughout molecular clouds, occurs in dense condensations located within these clouds. The physical conditions in these condensations are therefore critical input parameters for any theory of star formation.
A hydrodynamical model for the fragmentation of the W49A star-forming region
Authors: Lattanzio John , Keto Eric , Monaghan Joe
Published: June 2019

We present a 3-D hydrodynamical and radiative transfer simulation which suggests that the circular “necklace” of massive star formation in W49A may result from fragmentation via a ring instability during the collapse of a rotating cooling molecular cloud.
Physical parameters in extragalactic star forming regions
Authors: Mauersberger R. , Henkel C. , Sage L. J.
Published: June 2019

To use a molecule as a diagnostic of a single star forming region, one has to observe it in different transitions. That is especially true for galaxies, where the beam filling factor is small and unknown. From studies of Galactic objects, the CS molecule is a good tracer of dense gas. Toward the IR galaxies NGC 253, IC 342 and M 82, Mauersberger and Henkel (1989) observed the J=2—1, 3—2 and 5—4 transitions of CS at 3, 2 and 1.3 mm wavelength, repectively. They also measured emission of the isotope C34S, which has an abundance ∼ 1/23 that of the main isotope. This study revealed that the H2 densities in the circumnuclear gas exceed 104, and, in the case of NGC 253, 105 cm−3. In all three cases, the distribution of the dense gas traced out by CS follows the CO distribution.
Estimates of magnetic fields in interstellar gas clouds from 18-cm OH satellite lines
Authors: Rudnitskij G. M.
Published: June 2019

In interstellar clouds, where “thermal” /nonmaser/ OH emission in the 18-cm lines is observed, prominent anomalies of the intensities of the two satellite lines, 1612 and 1720 MHz, are often seen. If a cloud is observed against a background source of radio continuum, then one satellite may be in strong absorption, while the other one is in emission almost as strong as that in the main lines, 1665 and 1667 MHz. In those clouds, for which several positions were observed in the OH lines, the roles of the satellites are sometimes interchanged with the displacement along the cloud. At the same time, the main lines usually have the intensity ratio close to the equilibrium one. This behaviour indicates to deviations of the level populations of OH molecules from the Boltzmann ones.
Detection of Anisotropy in the Cosmic Microwave Background at Horizon and Sub-Horizon Scales with the BOOMERanG Experiment
Authors: de Bernardis P. , R. Ade P. A. , Bock J. J. , Bond J. R. , Borrill J. , Boscaleri A. , Coble K. , Crill B. P. , De Gasperis G. , De Troia G. , Farese P. C. , Ferreira P. G. , Ganga K. , Giacometti M. , Hivon E. , Hristov V. V. , Iacoangeli A. , Jaffe A. H. , Lange A. E. , Martinis L. , Masi S. , Mason P. , Mauskopf P. D. , Melchiorri A. , Miglio L. , Montroy T. , Netterfield C. B. , Pascale E. , Piacentini F. , Pogosyan D. , Pongetti F. , Prunet S. , Rao S. , Romeo G. , Ruhl J. E. , Scaramuzzi F. , Sforna D. , Vittorio N.
Published: June 2019

BOOMERanG has recently resolved structures on the last scattering surface at redshift ˜ 1100 with high signal to noise ratio. We review the technical advances which made this possible, and we focus on the current results for maps and power spectra, with special attention to the determination of the total mass-energy density in the Universe and of other cosmological parameters.
Developments at 30 GHz for Planck LFI
Authors: Davis R. J. , Roddis N. , Kettle D. , Winder F. , Wilkinson A. , Maddison B. , Hoyland R. , Artal E. , Martinez E. , Castelli C.
Published: June 2019

Jodrell Bank Observatory is responsible for the Front end modules (FEMs) for 30 GHz for LFI, with IAC being responsible for the hybrids and any phase switch. The University of Cantabria are responsible for the Back end modules (BEMs). Developments have been made to test prototypes both warm and cold for the FEMs. This is evolving towards flight hardware through an elegant breadboard phase EBB. Results of system performance show both white noise and 1/f characteristics.
Estimation of Signal and Noise Parameters from CMB Polarization Observations
Authors: Naselsky P. , Novikov D. , Novikov I. , Silk J.
Published: June 2019

We propose a technique for determination of the spectral parameters of the cosmological signal and pixel noise using observational data on CMB polarization without any additional assumptions. We introduce the notion of so called crossing points in the observational maps and derive the theoretical dependence of the total number of crossing points at different level of the polarization. Finally, we use the statistics of the signal in the vicinities of the singular points, where the polarization of the pure CMB vanishes to correct the final result.
Properties of the Dark Energy
Authors: Garnavich Peter M. , Wang Yun.
Published: June 2019

A non-zero cosmological constant is only one of many possible explanations for the observed accelerating expansion of the Universe. Any smoothly distributed, “dark” energy with a significant negative pressure can drive the acceleration. One possible culprit is a dynamical scalar field, but there are many less popular models such as tangled cosmic strings or domain walls. Soon theorists are likely to think up a number of new energies that can accelerate the expansion, meaning that only better observations can solve this question. Dark energy can be parameterized by its equation of state, w = p/ρ, which in the most general form can vary over time. Unlike the CMB, supernova observations cover a range of redshift so they can, in principle, probe the variation in the equation of state of the unknown component. The current SN observations loosely constrain the equation of state to w < −0.6, ruling out non-intercommuting strings and textures (w = −1/3), but consistent with a cosmological constant (w = −1). The constraints achievable from future large SN surveys are limited by our ability to understand systematic effects in SN Ia luminosities. But a large sample of supernovae reaching out to z ˜ 2 should at least discriminate between a cosmological constant and a dynamical scalar field as the source of the observed acceleration.
The Mass Density of the Universe
Authors: Bahcall Neta A.
Published: June 2019

One of the most fundamental questions in cosmology is: How much matter is there in the Universe and how is it distributed? Here I show that several independent measures-including those utilizing clusters of galaxies-all indicate that the mass-density of the Universe is low-only ˜20% of the critical density. Recent measurements of the mass-to-light function-from galaxies, to groups, clusters, and superclusters-provide a powerful new measure of the universal density. The results reveal a low density of 0.16±0.05 the critical density. The observations suggest that, on average, the mass distribution follows the light distribution on large scales. The results, combined with the recent observations of high redshift supernovae and the spectrum of the CMB anisotropy, suggest a Universe that has low density (Ωm ⋍0.2), is flat, and is dominated by dark energy.
CMB Analysis of Boomerang & Maxima & the Cosmic Parameters {Ωtot,Ωbh2, Ωcdmh2, ΩΛ, ns}
Authors: Richard Bond J. , Ade P. A. R. , Balbi A. , Bock J. J. , Borrill J. , Boscaleri A. , Coble K. , Crill B. P. , de Bernardis P. , Farese P. , Ferreira P. G. , Ganga K. , Giacometti M. , Hanany S. , Hivon E. , Hristov V. V. , Iacoangeli A. , Jaffe A. H. , Lange A. E. , Lee A. T. , Martinis L. , Masi S. , Mauskopf P. D. , Melchiorri A. , Montroy T. , Netterfield C. B. , Oh S. , Pascale E. , Piacentini F. , Pogosyan D. , Prunet S. , Rabii B. , Rao S. , Richards P. L. , Romeo G. , Ruhl J. E. , Scaramuzzi F. , Sforna D. , Sigurdson K. , Smoot G. F. , Stompor R. , Winant C. D. , Wu J. H. P.
Published: June 2019

We show how estimates of parameters characterizing inflation-based theories of structure formation localized over the past year when large scale structure (LSS) information from galaxy and cluster surveys was combined with the rapidly developing cosmic microwave background (CMB) data, especially from the recent Boomerang and Maxima balloon experiments. All current CMB data plus a relatively weak prior probability on the Hubble constant, age and LSS points to little mean curvature (Ωtot = 1.08±0.06) and nearly scale invariant initial fluctuations (ns = 1.03±0.08), both predictions of (non-baroque) inflation theory. We emphasize the role that degeneracy among parameters in the Lpk = 212 ± 7 position of the (first acoustic) peak plays in defining the Ωtot range upon marginalization over other variables. Though the CDM density is in the expected range (Ωcdmh2 = 0.17 ± 0.02), the baryon density Ωbh2 = 0.030 ± 0.005 is somewhat above the independent 0.019 ± 0.002 nucleosynthesis estimates. CMB+LSS gives independent evidence for dark energy (ΩΛ = 0.66 ± 0.06) at the same level as from supernova (SN1) observations, with a phenomenological quintessence equation of state limited by SN1+CMB+LSS to wQ < −0.7 cf. the wQ=−1 cosmological constant case.
The CLASS Gravitational Lens Search
Authors: Browne I. W. A. , Myers S. T.
Published: June 2019

To exploit gravitational lensing for cosmology large, reliable and statistically complete surveys are required. With the Cosmic Lens All-Sky Survey (CLASS) we have set out to achieve these goals. We pre-select targets to be flat spectrum radio sources and map every source with the VLA at 200mas resolution. Candidates having multiple compact components with flux density ratios ≤10:1 and separation in the range 0.3 to 15 arcsec are followed up with high resolution MERLIN and VLBA observations, eliminating those candidates which do not match strictly defined surface brightness and morphological criteria. A complete sample of 11685 sources have been surveyed and nineteen lens systems have been found.
A Robust Technique for Estimating Cosmological Parameters
Authors: Hendry Martin A. , Rauzy Stéphane
Published: June 2019

We present a new ROBUST technique for extracting information from galaxy surveys which allows determination of cosmological parameters free of almost any model assumptions concerning the galaxy luminosity function and spatial clustering. We illustrate ROBUST by estimating H0 and the linear bias parameter, β, from recent redshift-distance data.
Constraints on the Tensor Mode from Large Scale Structure Observations
Authors: Novosyadlyj B. , Durrer R. , Apunevych S.
Published: June 2019

Observational data on the large scale structure (LSS) of the Universe are used to establish an upper limit for the amplitude of the tensor mode marginalized over all other cosmological parameters within the class of adiabatic inflationary models. It is shown that the upper 1σ limit for the contribution of a tensor mode to the COBE DMR data is T/S < 1.
The “still point” cosmology
Authors: Shevchenko Ivan I.
Published: June 2019

Recent results on supernovae as standard candles (Riess et al. 1998; Perlmutter et al. 1999) and on CMB anisotropy (Lineweaver 1998) indicate that ΩM ≍ 0.3-0.4, Ωv ≍ 0.6-0.7, ΩM + Ωv ≍ 1. By definition, ΩM = ρM/ρcr, ΩV = ρv/ρcr, where ρM is the matter density, ρv is the vacuum density; the critical density ρcr = 3H2/8πG; H is the Hubble parameter, G is the gravitational constant. In the standard Friedmann-Lemaître cosmologies, these results seriously constrain the non-dimensional cosmological constant (as defined below): Δ ≫ 1, meaning that the Universe expands forever. If a scalar field is present, the future evolution may be different.
Effect of Spin-Gravity Interaction on the Cosmological Parameters
Authors: Wanas M. I.
Published: June 2019

Cosmological information is usually carried by, and extracted from massless spinning particles, “carriers of cosmological information”. The photon (spin 1-particle) is a good candidate representing one type of these carriers. Recently, the neutrino (spin 1/2-particle) entered the playground as another type. We expect, in the near future, that a third type of carriers, the graviton (spin 2-particle), to be used for extracting cosmological information. Two factors affect the properties of these carriers. The first is the source of the carrier. The second factor is the trajectory of the carrier, in the cosmic space, from its source to the receiver. The first factor implies the information carried, which reflect the properties of the source. The second factor represents the impact of the cosmic space-time on the properties of the carrier. So, information carried by these particles contain, a part connected to their sources, and another part related to the space-time through which these particles traveled.
The Spectral Index of the Galactic Foreground Affecting CMB Measurements
Authors: Zannoni M. , Battistelli E. S. , Boella G. , Gervasi M. , Sironi G.
Published: June 2019

We present results of measurements of the spectral index of the Galactic Diffuse emission (GDE), an information essential to evaluate the contamination of measured properties of the CMB by foregrounds.
H2O maser emission from bright rimmed globules
Authors: Valdettaro Riccardo , Palla Francesco , Cesaroni Riccardo , Testi Leonardo , Tofani Gianni
Published: June 2019

We report the results of a multi-epoch campaign of water maser observations of Bright Rimmed Globules (BRCs) associated with IRAS point sources. We have observed all of the 44 BRCs listed by Sugitani et al. (1991), visible in the northern hemisphere. With the exception of one globule, IC 1396N, we did not detect water maser emission in any of the targets. This negative result is somewhat surprising, if the suggestion of induced massive star formation in BRCs is correct. In contrast, we believe that newly formed stars inside BRCs tend to be of low luminosity and the occurrence of H2O maser emission is rare, episodic, and highly variable.
Statistics of the 6.7 GHz methanol maser variability from the Toruń survey
Authors: Niezurawska Anna , Szymczak Marian , Hrynek Grzegorz , Kus Andrzej J.
Published: June 2019

A sample of 174 methanol sources has been observed with the 32 m Toruń radio telescope at four or five epochs separated by 3-7 months. Observations of the 6.7 GHz maser line revealed that about 80% of sources are variable. 20% of sources showed strong variations of the integrated flux density usually on time-scales of 5-12 months. These variations were associated with strong changes in the relative intensities of maser features. Methanol emission from five sources disappeared. The time-scales of variability were longer than 12 months for only 23% of variable sources. It is suggested that the variability of methanol emission is related to the dynamics of the maser regions.