- ID:
- ivo://CDS.VizieR/J/A+A/600/A85
- Title:
- He-like ions (Z=20-42) effective collision strengths
- Short Name:
- J/A+A/600/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral lines of He-like ions are among the most prominent features in X-ray spectra from a large variety of astrophysical and high-temperature fusion plasmas. A reliable plasma modeling and interpretation of the spectra require a large amount of accurate atomic data related to various physical processes. In this paper, we focus on the electron-impact excitation (EIE) process. We adopted the independent process and isolated resonances approximation using distorted waves (IPIRDW). Resonant stabilizing transitions and decays to lower-lying autoionizing levels from the resonances are included as radiative damping. To verify the applicability of the IPIRDW approximation, an independent Dirac R-matrix calculation was also performed. The two sets of results show excellent agreement. We report electron impact excitation collision strengths for transitions among the lowest 49 levels of the 1snl(n<=5,l<=(n-1)) configurations in He-like ions with 20<=Z<=42. The line ratios R and G are calculated for Fe XXV and Kr XXXV.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/643/A130
- Title:
- Heliocentric minima for 14 eclipsing binaries
- Short Name:
- J/A+A/643/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The available minima timings of 14 selected eclipsing binaries (V1297 Cas, HD 24105, KU Aur, GU CMa, GH Mon, AZ Vel, DI Lyn, DK Her, GQ Dra, V624 Her, V1134 Her, KIC 6187893, V1928 Aql, V2486 Cyg) were collected and analyzed. Using the automatic telescopes, surveys, and satellite data, we derived more than 2500 times of eclipses, accompanied with our own ground-based observations. These data were used to detect the period variations in these multiple systems. The eclipse timing variations were described using the third-body hypothesis and the light-time effect. Their respective periods were derived as 2.5, 16.2, 27, 20, 64, 5.6, 22, 115, 27, 42, 6.9, 11.2, 4.1, and 8.4 years for these systems, respectively. The predicted minimal mass of the third body was calculated for each of the systems, and we discuss here their prospective detectability. The light curves of HD 24105, GH Mon, DK Her, V1134 Her, KIC 6187893, V1928 Aql, and V2486 Cyg were analyzed using the PHOEBE program, resulting in physical parameters of the components. Significant fractions of the third light were detected during the light-curve analysis, supporting our hypothesis of the triple-star nature of all these systems. The majority of these systems (nine out of 14) were already known as visual doubles. Our study shifts them to possible quadruples, what makes them even more interesting.
- ID:
- ivo://CDS.VizieR/J/A+A/407/31
- Title:
- Heliocentric radial velocities in Abell 376
- Short Name:
- J/A+A/407/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a dynamical analysis of the galaxy cluster Abell 376 based on a set of 73 velocities, most of them measured at Pic du Midi and Haute-Provence observatories and completed with data from the literature. Data on individual galaxies are presented and the accuracy of the determined velocities is discussed as well as some properties of the cluster. We obtained an improved mean redshift value z=0.0478^+0.005_-0.006_ and velocity dispersion {sigma}=852^+120^_-76_km/s. Our analysis indicates that inside a radius of ~900h_70_^-1^kpc (~15-arcmin) the cluster is well relaxed without any remarkable feature and the X-ray emission traces fairly well the galaxy distribution. A possible substructure is seen at 20-arcmin from the centre towards the Southwest direction, but is not confirmed by the velocity field. This SW clump is, however, kinematically bound to the main structure of Abell 376. A dense condensation of galaxies is detected at 46 arcmin (projected distance 2.6h_70_^-1^Mpc) from the centre towards the Northwest and analysis of the apparent luminosity distribution of its galaxies suggests that this clump is part of the large scale structure of Abell 376. X-ray spectroscopic analysis of ASCA data resulted in a temperature kT=4.3+/-0.4keV and metal abundance Z=0.32+/-0.08Z_{sun}. The velocity dispersion corresponding to this temperature using the T_X_-{sigma} scaling relation is in agreement with the measured galaxies velocities.
- ID:
- ivo://CDS.VizieR/J/MNRAS/482/4174
- Title:
- Heliocentric radial velocities of R CrB
- Short Name:
- J/MNRAS/482/4174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radial-velocity observations made on more than a thousand nights are presented for the type star of the R Coronae Borealis (RCB) class. There are four principal sources: the Lick Observatory (1950 to 1953), the original Cambridge radial-velocity spectrometer (1968 to 1991), and the Haute-Provence and Cambridge Coravels (1986 to 1998 and 1997 to 2007, respectively). In the case of the last set the size (equivalent width) and width (expressed as if Vsin(i)) of the Coravel cross-correlation (dip) profiles are also given, and the variation and complexity of those profiles are discussed. Although there is often evidence of cyclical behaviour in radial velocity, no coherent periodicity is found in any of the series. From time to time, and especially over 100 days before the great decline of 2007, the atmosphere was highly disturbed, with evidence of high-velocity components. We suggest that those are associated with large turbulent elements and result in mass ejection to sufficient distances for the formation of soot and other solids and thus the initiation of RCB-type declines. We associate the changes in light and radial velocity near maximum light primarily with the combined effect of such turbulent elements, and not with coherent pulsation. There is some evidence for a variation in the mean radial velocity on a time scale of about ten thousand days.
- ID:
- ivo://padc.obspm.helio/hfc1ar/q/epn_core
- Title:
- Heliophysics Feature Catalogue: Active regions
- Short Name:
- HFC1AR
- Date:
- 08 Oct 2024 04:30:31
- Publisher:
- Paris Astronomical Data Centre
- Description:
- Active regions of the Sun from Heliophysics Feature Catalogue (HFC).
- ID:
- ivo://CDS.VizieR/J/A+A/619/A99
- Title:
- Helioseismic measurements of solar meridional flow
- Short Name:
- J/A+A/619/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The solar meridional flow is an essential ingredient in flux-transport dynamo models. However, no consensus on its subsurface structure has been reached. We merge the data sets from SOHO/MDI and SDO/HMI with the aim of achieving a greater precision on helioseismic measurements of the subsurface meridional flow. The south-north travel-time differences are measured by applying time-distance helioseismology to the MDI and HMI medium-degree Dopplergrams covering May 1996-April 2017. Our data analysis corrects for several sources of systematic effects: P-angle error, surface magnetic field effects, and center-to-limb variations. For HMI data, we used the P-angle correction provided by the HMI team based on the Venus and Mercury transits. For MDI data, we used a P-angle correction estimated from the correlation of MDI and HMI data during the period of overlap. The center-to-limb effect is estimated from the east-west travel-time differences and is different for MDI and HMI observations. An interpretation of the travel-time measurements is obtained using a forward-modeling approach in the ray approximation. In the latitude range 20{deg}-35{deg}, the travel-time differences are similar in the southern hemisphere for cycles 23 and 24. However, they differ in the northern hemisphere between cycles 23 and 24. Except for cycle 24's northern hemisphere, the measurements favor a single-cell meridional circulation model where the poleward flows persist down to ~0.8R_{sun}_, accompanied by local inflows toward the activity belts in the near-surface layers. Cycle 24's northern hemisphere is anomalous: travel-time differences are significantly smaller when travel distances are greater than 20{deg}. This asymmetry between northern and southern hemispheres during cycle 24 was not present in previous measurements, which assumed a different P-angle error correction where south-north travel-time differences are shifted to zero at the equator for all travel distances. In our measurements, the travel-time differences at the equator are zero for travel distances less than ~30{deg}, but they do not vanish for larger travel distances. This equatorial offset for large travel distances need not be interpreted as a deep cross-equator flow; it could be due to the presence of asymmetrical local flows at the surface near the end points of the acoustic ray paths. The combined MDI and HMI helioseismic measurements presented here contain a wealth of information about the subsurface structure and the temporal evolution of the meridional circulation over 21 years. To infer the deep meridional flow, it will be necessary to model the contribution from the complex time-varying flows in the near-surface layers.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A141
- Title:
- Helium-like ions with Z=10-36 transition rates
- Short Name:
- J/A+A/592/A141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Helium-like ions provide an important X-ray spectral diagnostics in astrophysical and high-temperature fusion plasmas. An interpretation of the observed spectra provides information on temperature, density, and chemical compositions of the plasma. Such an analysis requires information for a wide range of atomic parameters, including energy levels and transition rates. Our aim is to provide a set of accurate energy levels and transition rates for helium-like ions with Z=10-36. The second-order many-body perturbation theory (MBPT) was adopted in this paper. To support our MBPT results, we performed an independent calculation using the multiconfiguration Dirac-Hartree-Fock (MCDHF) method.
- ID:
- ivo://CDS.VizieR/J/MNRAS/409/582
- Title:
- Helium-rich subluminous B stars abundances
- Short Name:
- J/MNRAS/409/582
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The connection between helium-rich hot subdwarfs of spectral types O and B (He-sdB) has been relatively unexplored since the latter were found in significant numbers in the 1980s. In order to explore this connection further, we have analysed the surface composition of six He-sdB stars, including LB 1766, LB 3229, SB 21 (= Ton-S 137 = BPS CS 29503-0009), BPS CS 22940-0009, BPS CS 29496-0010 and BPS CS 22956-0094.
- ID:
- ivo://CDS.VizieR/J/ApJ/885/74
- Title:
- 1340 Helium rich white dwarfs in the Gaia era
- Short Name:
- J/ApJ/885/74
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- We present an analysis of 1023 DBZ/DZ(A) and 319 DQ white dwarf stars taken from the Montreal White Dwarf Database. This represents a significant increase over the previous comprehensive studies on these types of objects. We use new trigonometric parallax measurements from the Gaia second data release, together with photometry from the Sloan Digital Sky Survey, Pan-STARRS, Gaia, or BVRI from the literature, which allow the determination of the mass for the majority of the objects in our sample. We use the photometric and spectroscopic techniques with our recently improved model atmospheres code, which include high-density effects, to accurately determine the effective temperature, surface gravity, and heavy-element abundances for each object. We study the abundance of hydrogen in DBZ/DZ white dwarfs and the properties of the accreted planetesimals. We explore the nature of the second sequence of DQ stars using proper motions from Gaia and highlight evidence of crystallization in massive DQ stars. We also present mass distributions for both spectral types. Finally, we discuss the implications of our findings in the context of the spectral evolution of white dwarfs and provide the atmospheric parameters for each star.
8140. HELLAS2XMM survey. IV.
- ID:
- ivo://CDS.VizieR/J/A+A/409/79
- Title:
- HELLAS2XMM survey. IV.
- Short Name:
- J/A+A/409/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the photometric and spectroscopic identification of 122 X-ray sources recently discovered by XMM-Newton in the 2-10keV band (the HELLAS2XMM 1dF sample). Their flux cover the range 8x10^-15^-4x10^-13^erg/cm^2^/s and the total area surveyed is 0.9 square degrees. One of the most interesting results (which is found also in deeper surveys) is that about 20% of the hard X-ray selected sources have an X-ray to optical flux ratio (X/O) ten times or more higher than that of optically selected AGN. Unlike the faint sources found in the ultra-deep Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes more than one order of magnitude lower than the HELLAS2XMM survey sources, many of the extreme X/O sources in our sample have R<~25 and are therefore accessible to optical spectroscopy. We report the identification of 13 sources with X/O>~10 (to be compared with 9 sources known from the deeper, pencil-beam surveys). Eight of them are narrow line QSO (seemingly the extension to very high luminosity of the type 2 Seyfert galaxies), four are broad line QSO. The results from our survey are also used to make reliable predictions about the luminosity of the sources not yet spectroscopically identified, both in our sample and in deeper Chandra and XMM-Newton samples. We then use a combined sample of 317 hard X-ray selected sources (HELLAS2XMM 1dF, Chandra Deep Field North 1Msec, Chandra SSA13 and XMM-Newton Lockman Hole flux limited samples), 221 with measured redshifts, to evaluate the cosmological evolution of the hard X-ray source's number and luminosity densities.