Counterparts Of Sources Research Articles

Assisted stellar suicide in V617 Sagittarii

Context.V617 Sgr is a V Sagittae star – a group of binaries thought to be the galactic counterparts of the Compact Binary Supersoft X-ray Sources – CBSS. Aims.To check this hypothesis, we measured the time derivative of its orbital period. Methods.Observed timings of eclipse minima spanning over 30 000 orbital cycles are presented. Results.We found that the orbital period evolves quite rapidly: years. This is consistent with the idea that V617 Sgr is a wind driven accretion supersoft source. As the binary system evolves with a time-scale of about one million years, which is extremely short for a low mass evolved binary, it is likely that the system will soon end either by having its secondary completely evaporated or by the primary exploding as a supernova of type Ia. Conclusions.

MAMBO 1.2 mm Observations of B z K -selected Star-forming Galaxies at z ~ 2

We present MAMBO 1.2 mm observations of five BzK-preselected vigorous starburst galaxies at z ~ 2. Two of these were detected at more than 99.5% confidence levels, with 1.2 mm fluxes around 1.5 mJy. These millimeter fluxes imply vigorous activity with star formation rates (SFRs) of ?500-1500 M? yr-1, which were also confirmed by detections at 24 ?m with the Multiband Imaging Photometer on Spitzer (MIPS). The two detected galaxies are the ones in the sample with the highest SFRs estimated from the rest-frame UV, and their far-IR-derived and UV-derived SFRs agree reasonably well. This is different from local ultraluminous infrared galaxies (ULIRGs) and high-z submillimeter/millimeter-selected galaxies, for which the UV is reported to underestimate SFRs by factors of 10-100, but similar to the average BzK ULIRG at z ~ 2. The two galaxies detected at 1.2 mm are brighter in K than the typical NIR counterparts of MAMBO and SCUBA sources, implying a significantly different K-band-to-submillimeter/millimeter flux ratio as well. This suggests a scenario in which z ~ 2 galaxies, after their rapid (sub)millimeter-bright phase that is opaque to optical/UV light, evolve into a longer lasting phase of K-band-bright and massive objects. Targeting the most UV-active BzK galaxies could yield substantial detection rates at submillimeter/millimeter wavelengths.

Controls on methanol and acetone in marine and continental atmospheres

We present a regional analysis of CH3OH and (CH3)2CO in the New England continental and coastal marine atmospheres. Vegetative emissions over land comprise 60–80% of the daily peak‐to‐peak differences in the diurnal cycles of these oxygenated hydrocarbons. In the morning downward mixing of remnant boundary layer air over land provides an additional source equal to more than half of the vegetative emission strength. The ocean is both a sink and a source of CH3OH and (CH3)2CO, with dry depositional losses 2‐fold greater than their source counterparts of 0.35 and 0.17 ppbv d−1 respectively. Anthropogenic emissions compensate for 59% and 52% of CH3OH and (CH3)2CO oceanic sink respectively, whereas over land this source is relatively small compared to substantial vegetative sources. Direct measurements of ocean‐ and land‐air fluxes of CH3OH and (CH3)2CO and boundary layer height are needed to better constrain their regional budgets.

Analysis of the open source software sector in China

Summary The paper describes the status and context of the Chinese Open Source Software (OSS) industry and ecosystem based on the analysis of the components of the China OSS Promotion Union. The analysis involves comparisons of several main Chinese developers of Linux operating system and makers of open source counterpart of the popular Microsoft Office package as well as several main Chinese OSS communities. Comparisons concern the technological and business aspect. The findings reveal peculiarities of the divergence of innovative activities of Chinese companies, as well as indicate that the strong government support may at the same time limit the technology selection under rigid competition, especially as foreign open source companies are found to be more focused on hobbyist developers and are able to maintain larger independent communities. Implications of the paper include the need to coordinate global development efforts and adjust science & technology policies in order to stimulate both the development and the diffusion of open source among Chinese companies and individual hobbyists.

Microquasar Models for 3EG J1828+0142 and 3EG J1735-1500

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box.

FIRBACK

We present a detailed study of the brighter (>$4\sigma$ detections) sources in the 170 μ m FIRBACK northern N1 ISO survey, with the help of complementary data in the optical, radio, and mid-IR domain. For 82% of them, an optical galaxy counterpart is identified, either as the unique source of the IR emission, or as part of a multiple identification. With less than 15% of AGNs, these sources are essentially local, moderate starbursters with a dominating cold dust component. They are therefore very similar to the galaxies in the IRAS Very Faint Survey or the ISO 170 μ m Serendipity Survey, and represent a population of cold galaxies rather neglected up to now. Their colours do not match those of the far-IR Cosmic IR Background (CIB), to which they contribute less than 5%. The bulk of the sources contributing to the CIB is thus to be searched for in more distant galaxies, possibly counterparts of the fainter FIRBACK sources still under study. These bright, local, galaxies however play an important role in the evolution of IR galaxies: they dominate the number counts at high 170 μ m fluxes, and represent half of the contribution at 250 mJy. Although not particularly massive (typically M * ), they form more stars than a typical spiral galaxy and many are bulge dominated, that could represent the remnant of a former merger. The fainter part of this population may represent the missing link with the higher- z sources found in sub-mm observations.

Identification of Optical Counterparts of ULX sources

Identification of Optical Counterparts of ULX sources

Search for new T Tauri stars in the Cepheus-Cassiopeia region

The Cepheus-Cassiopeia star-forming region has been searched for new T Tauri stars (TTSs) based on the ROSAT all sky survey (RASS). Optical spectroscopic observations were carried out toward 45 GSC stellar counterparts of RASS sources looking for the Li absorption line (6708 A), a sign of youth. The detection of this line resulted in finding 11 to 16 new TTSs in this region. Using follow-up optical photometric observations and evolutionary models these Li-rich stars are revealed to be young low-mass stars. The most of the young stars are separated from the $\element[][13]{CO}$ molecular clouds by ~10 pc, significantly more than in Chamaeleon. A group of the new TTSs are isolated from the CO clouds and distributed inside the previously determined CO void. Possible formation scenarios including the interaction with the supernova shock for the isolated TTSs are discussed.

Identifying Variable γ-ray Sources Through Radio Observations

We present preliminary results of a campaign undertaken with different radio interferometers to observe a sample of the most variable unidentified EGRET sources. We expect to detect which of the possible counterparts of the γ-ray sources (any of the radio emitters in the field) varies in time with similar timescales as the γ-ray variation. If the γ-rays are produced in a jet-like source, as we have modelled theoretically, synchrotron emission is also expected at radio wavelengths. Such radio emission should appear variable in time and correlated with the γ-ray variability.

Hot problems in astroparticle physics today

The goal of this paper is to point out and discuss several of the most important points still open in astroparticle physics today. Of course, this paper is not exhaustive because of essentially two reasons: the first due to my knowledge and the second to the reasonable length of the paper. However, I will try to remark those hot points which will be discussed in more details during the worksliop. 1 will outline the following items: 1) Introduction, 2) Cosmology, 3) Clusters of galaxies as γ-ray emitters, 4) Cosmic counterparts of γ-ray sources. 5) Active galactic nuclei and galactic collapsed objects: unified schemes, 6) Relativistic jets, 7) Gamma ray bursts. 8) X-ray binaries, 9) Neutrinos, 10) Some ideas on future missions. 11) Conclusions.

Li abundance in young PMS associations: AB Dor

We present stellar parameters and Li abundances for 21 stars of the young (∼50 Myears) AB Dor association, based on high-resolution spectra obtained with FEROS at the ESO 1.52m telescope and the Coude Spectrograph at the OPD 1.6m telescope. These results are part of an ongoing project for the determination of stellar parameters and abundances for a large sample of T Tauri and post-T Tauri stars in PMS associations identified on the Search for Associations Containing Young Stars survey. The sample consists of G, K and M stars counterparts of ROSAT bright sources. Since we expect Li depletion for the K and M stars, but small Li depletion for the G stars, we can compare the upper values of Li abundances for these stars with the one of the Galactic disk interstellar mean and at the same time provide constrains for the study of Li depletion on a chemically homogeneous high metallicity sample.

The Phoenix Deep Survey: Spectroscopic Catalog

The Phoenix Deep Survey is a multiwavelength survey based on deep 1.4 GHz radio imaging, reaching well into the sub-100 μJy level. One of the aims of this survey is to characterize the submillijansky radio population, exploring its nature and evolution. In this paper we present the catalog and results of the spectroscopic observations aimed at characterizing the optically bright (R 21.5 mag) counterparts of faint radio sources. Of 371 sources with redshift determination, 21% have absorption lines only, 11% show active galactic nucleus signatures, 32% are star-forming galaxies, 34% show narrow emission lines that do not allow detailed spectral classification (owing to poor signal-to-noise ratio and/or lack of diagnostic emission lines), and the remaining 2% are identified with stars. For the star-forming galaxies with a Balmer decrement measurement we find a median extinction of AHα = 1.9 mag, higher than that of optically selected samples. This is a result of the radio selection, which is not biased against dusty systems. Using the available spectroscopic information, we estimate the radio luminosity function of star-forming galaxies in two independent redshift bins at z ≈ 0.1 and 0.3, respectively. We find direct evidence for strong luminosity evolution of these systems consistent with L1.4 GHz ∝ (1 + z)2.7.

THE PROCUREMENT DECISION - "OPEN" OR "CLOSED" SOURCE SOFTWARE?

<div class="page" title="Page 1"><div class="layoutArea"><div class="column"><p><span>[</span><span>The merits of open source software, particularly in the context of Australian Government procurement, have been the subject of considerable debate in recent times. This paper provides an overview of the distinguishing features of open source software and considers the terms of the licence under which open source software is distributed. Consideration is also given to the merits of open source software through an examination of both the legal and tech- nical risks associated with the product. In concluding, it is determined that there is a positive argument for mandating open source software as a viable alternative to its closed source counterpart.</span><span>] </span></p></div></div></div>

The Nature of Ultraluminous X-Ray Sources

We present spectroscopic observations of six optical counterparts of ultraluminous X-ray sources (ULXs) around nearby galaxies. The spectra of the six objects show the presence of broad emission features. The identification of these allow us to classify all of the objects as quasars at higher redshift than their assigned parent galaxy. This is one of the first and largest identifications of such objects using unambigous optical spectral features. These results, in conjuction with previous similar identifications of other sources, indicate that high-redshift quasars represent an important fraction of cataloged ULX sources. We estimate the density of such sources and compare this with expectations for a population of randomly distributed background quasars.

High energy gamma ray counterparts of astrophysical sources of ultra-high energy cosmic rays

If ultra-high energy cosmic rays (UHECRs) are accelerated at astrophysical point sources, the identification of such sources can be achieved if there is some kind of radiation at observable wavelengths that may be associated with the acceleration and/or propagation processes. No radiation of this type has so far been detected or at least no such connection has been claimed. The process of photopion production during the propagation of UHECRs from the sources to the Earth results in the generation of charged and neutral pions. The neutral (charged) pions in turn decay to gamma quanta and electrons that initiate an electromagnetic cascade in the universal photon background. We calculate the flux of this gamma radiation in the GeV–TeV energy range and find that for source luminosities compatible with those expected from small scale anisotropies in the directions of arrival of UHECRs, the fluxes can be detectable by future Cerenkov gamma ray telescopes, such as VERITAS and HESS, provided the intergalactic magnetic field is not larger than ∼10 −10 Gauss and for source distances comparable with the loss length for photopion production.

A far-infrared view of the Lockman hole fromISO95-μm observations - II. Optical identifications and insights into the nature of the far-infrared sources

We present the optical identifications of a 95-μm ISOPHOT sample in the Lockman hole over an area of approximately half a deg2. The Rodighiero et al. catalogue includes 36 sources, making up a complete flux-limited sample for S95μm≥ 100 mJy. Reliable sources were detected, with decreasing but well-controlled completeness, down to S95μm≃ 20 mJy. We have combined mid-infrared (IR) and radio catalogues in this area to identify the potential optical counterparts of the far-IR sources. We found 14 radio and 13 15-μm associations, 10 of which have both associations. For the 11 sources with spectroscopic redshift, we have performed a spectrophotometric analysis of the observed spectral energy distributions (SEDs). Four of these 95-μm sources have been classified as faint IR (FIR) galaxies (LFIR < 1.e11 L⊙), six as luminous IR galaxies (LIRGs) and only one as an ultraluminous IR galaxy (ULIRG). We have discussed the redshift distribution of these objects, comparing our results with evolutionary model predictions 95 and 175 μm. Given their moderate distances (the bulk of the closest spectroscopically identified objects lying at z < 0.2), their luminosities and star formation rates (SFR; median value ∼ 10 M⊙ yr−1), the sources unveiled by ISOPHOT at 95 μm seem to correspond to the low redshift (z < 0.3) FIRBACK 175-μm population, composed of dusty, star-forming galaxies with moderate SFRs. We computed and compared different SFR estimators, and found that the SF derived from the bolometric IR luminosity is well correlated with that computed from the radio and mid-IR fluxes.

Automated Classification ofROSATSources Using Heterogeneous Multiwavelength Source Catalogs

We describe an on-line system for automated classification of X-ray sources, ClassX, and present preliminary results of classification of the three major catalogs of ROSAT sources, RASS BSC, RASS FSC, and WGACAT, into six class categories: stars, white dwarfs, X-ray binaries, galaxies, AGNs, and clusters of galaxies. ClassX is based on a machine learning technology. It represents a system of classifiers, each classifier consisting of a considerable number of oblique decision trees. These trees are built as the classifier is 'trained' to recognize various classes of objects using a training sample of sources of known object types. Each source is characterized by a preselected set of parameters, or attributes; the same set is then used as the classifier conducts classification of sources of unknown identity. The ClassX pipeline features an automatic search for X-ray source counterparts among heterogeneous data sets in on-line data archives using Virtual Observatory protocols; it retrieves from those archives all the attributes required by the selected classifier and inputs them to the classifier. The user input to ClassX is typically a file with target coordinates, optionally complemented with target IDs. The output contains the class name, attributes, and class probabilities for all classified targets. We discuss ways to characterize and assess the classifier quality and performance and present the respective validation procedures. Based on both internal and external validation, we conclude that the ClassX classifiers yield reasonable and reliable classifications for ROSAT sources and have the potential to broaden class representation significantly for rare object types.

High energy gamma ray counterparts of astrophysical sources of ultra-high energy cosmic rays

If ultra-high energy cosmic rays (UHECRs) are accelerated at astrophysical point sources, the identification of such sources can be achieved if there is some kind of radiation at observable wavelengths that may be associated with the acceleration and/or propagation processes. No radiation of this type has so far been detected or at least no such connection has been claimed. The process of photopion production during the propagation of UHECRs from the sources to the Earth results in the generation of charged and neutral pions. The neutral (charged) pions in turn decay to gamma quanta and electrons that initiate an electromagnetic cascade in the universal photon background. The ultra high energy protons interaction produces also electron positron pairs with typical energy of 700 TeV which initiate a faster electromagnetic cascade. We calculate the flux of the overall gamma radiation in the GeV-TeV energy range and find that for source luminosities compatible with those expected from small scale anisotropies in the directions of arrival of UHECRs, the fluxes can be detectable by future Cerenkov gamma ray telescopes, such as VERITAS and HESS for source distances comparable with the loss length for photopion production. The effects of a widespread extra-galactic magnetic field on the cascade flux are discussed for various intensities and simple configurations.

The cosmological significance of low surface brightness galaxies found in a deep blind neutral hydrogen survey

We have placed limits on the cosmological significance of gas-rich low surface-brightness (LSB) galaxies as a proportion of the total population of gas-rich galaxies by carrying out a very deep survey (HIDEEP) for neutral hydrogen (HI) with the Parkes multibeam system. Such a survey avoids the surface-brightness selection effects that limit the usefulness of optical surveys for finding LSB galaxies. To complement the HIDEEP survey we have digitally stacked eight 1-hour R-band Tech Pan films from the UK Schmidt Telescope covering 36 square degrees of the survey area to reach a very deep isophotal limit of 26.5 R mag/sq. arcsec. At this level, we find that all of the 129 HI sources within this area have optical counterparts and that 107 of them can be identified with individual galaxies. We have used the properties of the galaxies identified as the optical counterparts of the HI sources to estimate the significance of LSB galaxies (defined to be those at least 1.5 magnitudes dimmer in effective surface-brightness than the peak in the observed distribution seen in optical surveys). We calculate the contribution of LSB galaxies to the total number, neutral hydrogen density, luminosity density, baryonic mass density, dynamical mass density and cross-sectional area of gas-rich galaxies. We do not find any `Crouching Giant' LSB galaxies such as Malin 1, nor do we find a population of extremely low surface-brightness galaxies not previously found by optical surveys. Such objects must either be rare, gas-poor or outside the survey detection limits.

Infrared Array Camera (IRAC) Imaging of the Lockman Hole

IRAC imaging of a 4'7x4'7 area in the Lockman Hole detected over 400 galaxies in the IRAC 3.6 micron and 4.5 micron bands, 120 in the 5.8 micron, and 80 in the 8 micron bandin 30 minutes of observing time. Color-color diagrams suggest that about half of these galaxies are at redshifts 0.6<z<1.3 with about a quarter at higher redshifts (z>1.3). We also detect IRAC counterparts for 6 of the 7 SCUBA sources and all 9 XMM sources in this area. The detection of the counterparts of the SCUBA sources and galaxies at z>1.3 demonstrates the ability of IRAC to probe the universe at very high redshifts.