Uncertainties In Mass Estimates Research Articles

Unveiling pure-metal ejecta X-ray emission in supernova remnants through their radiative recombination continuum

Context. Spectral analysis of X-ray emission from ejecta in supernova remnants (SNRs) is hampered by the low spectral resolution of CCD detectors, which typically creates a degeneracy between the best-fit values of chemical abundances and the plasma emission measure. The combined contribution of shocked ambient medium and ejecta to the emerging X-ray emission further complicates the determination of the ejecta mass and chemical composition. This degeneracy leads to big uncertainties in mass estimates and can introduce a bias in the comparison between the ejecta chemical composition derived from the observations and the yields predicted by explosive nucleosynthesis models. Aims. We explore the capabilities of present and future spectral instruments with the aim of identifying a spectral feature that may allow us to discriminate between metal-rich and pure-metal plasmas in X-ray spectra of SNRs. Methods. We studied the behavior of the most common X-ray emission processes of an optically thin plasma in the high-abundance regime. We investigated spectral features of bremsstrahlung, radiative recombination continua (RRC), and line emission, by exploring a wide range of chemical abundances, plasma temperatures, and ionization parameters. We then synthesized X-ray spectra from a state-of-the-art 3D hydrodynamic simulation of Cas A, by using the response matrix from the Chandra ACIS-S charged-coupled device detector and that of the XRISM/Resolve X-ray calorimeter spectrometer. Results. We found that a bright RRC shows up when the plasma is made of pure-metal ejecta, and a high spectral resolution is needed to actually identify this ejecta signature. We tested and verified the applicability of our novel diagnostic tool and we propose a promising target for the future detection of such spectral feature: the southeastern Fe-rich clump of Cas A. Conclusions. While there is no way to unambiguously reveal pure-metal ejecta emission with CCD detectors, X-ray calorimeters will be able to pinpoint the presence of pure-metal RRC and to recover correctly absolute mass and the chemical composition of the ejecta, opening a new window on the link between progenitor star, supernova and SNRs.

A new method for determining the CO to H2 conversion factor for translucent clouds

In this paper we describe a new technique for obtaining the conversion factor between the molecular hydrogen column density and the CO(J = 1-0) integrated antenna temperature. This factor, typically known as X(sub CO) is often to be of order a few times 10(exp 20)/sq cm/K km/s) for the molecular clouds in the Galaxy and is one of the primary means of determining the molecular cloud mass from CO observations. However, for the low-extinction interstellar clouds known as the translucent molecular clouds, estimates of X(sub CO) vary by up to a factor of 60 depending on the object and techniques employed to calibrate X(sub CO). Since the cloud mass is directly proportional to X(sub CO) uncertainties in mass estimates of translucent clouds can be more than an order of magnitude. We calibrate the H2 content in translucent clouds by using the linear relationship between the CH and H2 column densities. The CH column density is readily determined from observations of the CH ground-state hyperfine main-line transition at 3335 MHz. Using CH as a surrogate tracer for H2 and CO(J = 1-0) observations of a sample of translucent and dark molecular clouds, we find a wide variation in values for X(sub CO). For translucent clouds, X(sub CO) ranges from 0.3 to 6.8 x 10(exp 20) and for dark clouds the values range from 0.8 to 8.6. Although the average values for both types of cloud are similar to the canonical value determined for the Galactic molecular cloud ensemble (2-4 x 10(exp 20)), the scatter in individual X(sub CO) values may indicate that X(sub CO) for a given translucent cloud cannot be determined a priori and must be obtained for each cloud so that a reliable mass determination may be made.

The mass of the Coma cluster

view Abstract Citations (177) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The mass of the Coma cluster. The, Lih Sin ; White, Simon D. M. Abstract The authors examine the uncertainties in mass estimates for the Coma cluster derived from position and velocity data for the galaxies. If the mass distribution is assumed to parallel the galaxy distribution, the total mass within 5.4h50-1 Mpc is 1.9×1015h50-1M_sun; to an accuracy of about 30% (for H0 = 50 h50 km/s/Mpc). However, if the form of the mass distribution is not constrained, the total mass in this region can range between 6×1014h50-1 M_sun; and 5×1015h50-1 M_sun;. Low-mass models have all the mass in the cluster core and require the galaxies to be on near circular orbits. High-mass models have weakly concentrated mass distributions and primarily radial orbits. Galaxy data alone are unlikely to be able to distinguish between these possibilities. Publication: The Astronomical Journal Pub Date: December 1986 DOI: 10.1086/114258 Bibcode: 1986AJ.....92.1248T Keywords: Astronomical Models; Galactic Clusters; Mass Distribution; Circular Orbits; Radial Velocity; Virial Theorem; Astrophysics; Clusters of Galaxies:Coma; Clusters of Galaxies:Masses; Masses:Clusters of Galaxies full text sources ADS | data products SIMBAD (1) NED (1)