Best-fit Temperature Research Articles

Subcluster mergers and galaxy infall in A2151

We have obtained a 12.5 ks image of the Hercules Cluster, A2151, with the ROSAT PSPC. Comparison of the optical and X-ray emission coincides with the highest-density peak in the distribution, and is bimodal. The northern subclummp, distinct in position and velocity, has no detectable X-ray gas. The eastern subclump, apparent in the optical contour map, is indistinguishable from the clump in velocity space, but is clearly visible in the X-ray image. X-ray spectra derived from the central peak of emission yield a best-fit temperature of 1.6 keV. The emission coincident with the eastern clump of galaxies is cooler, 0.8 keV, and is outside the 90% confidence intervals of the central peak temperature. We suggest that the eastern and central subclusters have recently undergone a merger event. The lack of X-ray emission to the north suggests that those galaxies do not form a physically distinct structure (i.e., they are not located within a distinct gravitational potential), but rather that they are falling into the cluster core along the filament defined by the Hercules Supercluster.

RE 0044+09: A new K dwarf rapid rotator with a white dwarf companion

We report the discovery of a new K dwarf rapid rotator with a potential white dwarf companion. The white dwarf accounts for over 90% of the observed extreme ultraviolet flux detected from this system. Analysis of ROSAT Wide Field Camera (WFC) and IUE data both suggest a white dwarf temperature of approximately 28,700 K. Optical photometry and the IUE long wavelength prime (LWP) spectrum (with the white dwarf contribution removed) imply that the late-type star has a spectral type of K1-3 V, and a distance of 55 +/- 5 pc. Using this distance, the observed IUE SWP flux, and the best-fit temperature results in a white dwarf radius of 0.0088 solar radius. The estimated white dwarf mass is then approximately 0.91 solar mass; somewhat over-massive compared to field white dwarfs. Optical photometry of the K star reveals a 'spot' modulation period of approximately 10 hr (now observed over 3 yr). However, radial velocity observations have revealed no significant variations. Spectroscopic observations place a low limit on the lithium abundance, but do show rapid rotation with a v sin i of 90 +/- 10 km/s. The K star was detected as a radio source at 3.6 cm (on two occasions) and 6 cm by the Very Large Array (VLA). The most likely evolutionary scenario is that the K star and hot white dwarf from either a wide binary or common proper motion pair with an age of 0.1-0.1 Gyr-consistent with the evolutionary timescale of the white dwarf and the rapid rotation of the K star. However, from the proper motion of the K star, this system does not seem to be associated with any of the known young stellar groups.

Hubble Space Telescope Goddard high-resolution spectrograph H2 rotational spectra of Jupiter's aurora

We have observed the emission spectrum from Jupiter's north auroral atmosphere with 0.57 A spectral resolution over 1204-1241 A. Bright emissions have been detected from 50 deg to 60 deg latitude at locations consistent with 6 to 30 R (sub J) auroral ovals, with much fainter emissions away form the auroral ovals. The emission spectrum is well fitted by both laboratory spectra and theoretical models of optically thin electron excited H2, with added Doppler-broadened Lyman Alpha emission. The observed Lyman Alpha emission wings extend more than 1 A from line center and appear correlated in strength with the H2 brightness. Individual rotational lines in the H2 Werner band system are resolved, allowing a determination of the H2 rotational temperature at the altitude of the emission. We derive best-fit temperatures from 400-450 to 700-750 K, with the auroral emission layer temperature changing either across the auroral oval or over several days' time. These observations demonstrate for the first time the ability to measure the observed rapid H2 temperature variations across Jupiter's auroral atmosphere.

Effect of the Slit Function of the Detection System and a Fast-Fitting Algorithm on Accuracy of CARS Temperature

The effect of the erroneous functional forms of the slit functions on the best-fit temperature in CARS (coherent anti-Stokes Raman spectroscopy) thermometry has been investigated. When the shape of the slit function is described as a Lorentzian or a Gaussian function and its width adjusted with the room-temperature CARS spectrum, the maximum systematic errors due to the slit functions reach 1.5–2.5% in the temperature range from 300 to 2100 K. A fast-fitting algorithm exponentially interpolating the CARS spectrum at an intermediate temperature with two precalculated spectra has been proposed, and its validity has been assessed by calculating the error due to the fitting algorithm.

ROSAT observations of ${\rm PSR}\ 0950+08$

We report on observations of the radio pulsar PSR 0950+08 obtained using the Position Sensitive Proportional Counter and Wide Field Camera on board ROSAT. The background-corrected count rate is determined to be 0.0069±0.0012 count s −1 in the 0.08-2.4 keV energy range. The derived spectrum could be fitted to both blackbody and power-law models modified by interstellar absorption. The best-fitting surface temperature of 2.6×10 6 K and the age of PSR 0950+08 (∼1.7×10 7 yr) imply that some form of heating process is occurring if the emission is thermal. The small implied size of the emission region (radius ≤20 m) points towards some form of polar-cap heating, although of the models available only the slot-gap model proposed by Arons can perhaps account for the observed luminosity

Diffuse X-ray emission from the Dumbbell Nebula?

We have analyzed ROSAT Position Sensitive Proportional Counter pointed observations of the Dumbbell Nebula and find that the previously reported 'extended' X-ray emission is an instrumental electronic ghost image at the softest energy band. At slightly higher energy bands, the image of the Dumbbell is not very different from that of the white dwarf HZ43. We conclude that the X-ray emission of the Dumbbell Nebula comes from its central star. A blackbody model is fitted to the spectrum and the best-fit temperature of not greater than 136,000 +/- 10,000 K is in excellent agreement with the Zanstra temperatures.

Diffuse X-ray emission from the NGC 2300 group of galaxies - Implications for dark matter and galaxy evolution in small groups

The discovery of diffuse X-ray emission from the NGC 2300 group of galaxies using the ROSAT Position Sensitive Proportional Counter is reported. The gas distributions is roughly symmetric and extends to a radius of at least 0.2/h(50) Mpc. A Raymond-Smith hot plasma model provides an excellent fit the X-ray spectrum with a best-fit value temperature of 0.9 + -/15 or - 0.14 keV and abundance 0.06 + 0/.12 or - 0.05 solar. The assumption of gravitational confinement leads to a total mass of the group of 3.0 + 0.4 or - 0.5 x 10 exp 13 solar. Baryons can reasonably account for 4 percent of this mass, and errors could push this number not higher than 10-15 percent. This is one of the strongest pieces of evidence that dark matter dominates small groups such as this one. The intragroup medium in this system has the lowest metal abundance yet found in diffuse gas in a group or cluster.

Cooling rate of an active Hawaiian lava flow from nighttime spectroradiometer measurements

A narrow‐band spectroradiometer has been used to make nighttime measurements of the Phase 50 eruption of Pu'u O'o, on the East Rift Zone of Kilauea Volcano, Hawaii. On February 19, 1992, a GER spectroradiometer was used to determine the cooling rate of an active lava flow. This instrument collects 12‐bit data between 0.35 to 3.0 μm at a spectral resolution of 1 – 5 nm. Thirteen spectra of a single area on a pahoehoe flow field were collected over a 59 minute period (21:27 – 22:26 HST) from which the cooling of the lava surface has been investigated. A two‐component thermal mixing model [Flynn, 1992] applied to data for the flow immediately on emplacement gave a best‐fit crustal temperature of 768°C, a hot component at 1150°C, and a hot radiating area of 3.6% of the total area. Over a 52‐minute period (within the time interval between flow resurfacings) the lava flow crust cooled by 358°C to 410°C at a rate that was as high as 15°C min−1. Our observations have significance both for satellite observations of active volcanoes and for numerical models of the cooling of lava flows during their emplacement.

An ionized accretion disk in Cygnus X-1

Results of an analysis of archival Exosat and HEAO 1-A2 observations of Cyg X-1 are presented. It is found, in agreement with Ebisawa (1991), that the X-ray spectrum of Cyg X-1 exhibits a 'high-energy excess' above 8 keV, similar to that seen in Ginga spectra of AGN. It is shown, on the basis of a likelihood ratio test, that the data are significantly better fit by a Compton reflection model than by a partial covering model. Even with the energy resolution of the Exosat GSPC, it is found that the derived iron line energy and shape are very dependent on the continuum model used. The best-fit temperature for a Suniaev-Titarchuk Comptonization model is found to be significantly larger than that found in previous analyses based primarily on data in the 30-140 keV band. This suggests that the 5-50 keV continuum is not well fit by the same spectrum form applicable at high energies and that a multiple temperature thermal Compton model is necessary to fit the broadband data.

Phase constitution and thermal expansion ofYBa2Cu3O7−δsingle crystals

We present an x-ray diffraction study of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ single crystals. High-resolution scans reveal two orthorhombic phases with different lattice constants but a common orientation indicating a phase separation into phases with $\ensuremath{\delta}\ensuremath{\approx}0.0 \mathrm{and} 0.3$. Thermal expansions of the unit-cell parameters of both phases measured between 10 and 300 K were fit using a quasiharmonic approximation giving a best-fit Debye temperature of 370\ifmmode\pm\else\textpm\fi{}5 K. The measured orthorhombicities were found to change smoothly through the superconducting transition temperature without any anomaly.

Electron temperatures in the galactic HII regions Orion A and Orion B from radio continuum observations at 0.33 and 10.7 GHz

We have made arcminute resolution maps of Orion A and Orion B at 0.33 GHz where the central parts of both nebulae are highly opaque and at 10.7 GHz where they are fully transparent. The 0.33 GHz maps yield direct estimates of electron temperature towards the peaks of these nebulae, whereas the 10.7 GHz maps are used to estimate ‘best-fit isothermal temperatures’ using an improved version of the approach followed in the past. Based on radio continuum data alone, these two types of estimates provide evidence for a decrease in the electron temperature away from the core region, at least for Orion A.

Single-pulse broadband rotational coherent anti-Stokes Raman-scattering thermometry of cold N_2 gas

Coherent anti-Stokes Raman scattering (CARS) from the pure rotational Raman lines of N(2) gas is employed to measure the instantaneous (10-nsec) rotational temperature of the gas at room temperature and below. An entire rotational CARS spectrum is generated by a single laser pulse using a broad-bandwidth dye laser and is recorded on an optical multichannel analyzer. A best-fit temperature is obtained for individual experimental spectra by comparison with calculated spectra. Good agreement between CARS temperatures and thermocouple temperatures is observed.

X-ray line emission from the Cygnus Loop

The HEAO 1 satellite has observed the X-ray spectrum of the Cygnus Loop in the 0.1-2.0 keV band. The observed count-rate spectrum is deconvolved by the Kahn and Blissett technique to demonstrate conclusively the presence of oxygen- and iron-line emission between 0.6 and 0.9 keV. The spectrum has been fitted with single- and two-component Raymond-Smith plasma emission models. The best-fit dominant X-ray temperature is approximately 3,200,000 K, and the best-fit interstellar column density is approximately a few times 10 to the 20th/sq cm.

The transient periodic X-ray source in Taurus, A0535+26

Eighteen X-ray light curves of the 104-sec periodicity in the Taurus X-ray nova A 0535+26 are analyzed which were obtained by SAS-3 in six energy intervals between 1 and 35 keV during the period from May 30 to June 2, 1975. It is shown that the pulse structure is relatively simple at energies above 19 keV, but develops a complex series of five irregularly spaced maxima at lower energies. The energy spectrum averaged over the 104-sec period is found to be extremely hard, with a best-fit temperature of about 30 keV for the exponential spectrum, an excess at about 15 keV, and a steepening above 20 keV. It is suggested that A 0535+26 may be a compact object in a binary system containing the peculiar Be star HDE 245770. The transient behavior could arise due to episodic mass loss by the primary or because the compact object is in a highly eccentric orbit about the companion, with appreciable mass transfer occurring only at periastron.

Effect of Gaunt Factors on Analysis of X-Ray Spectra: Viability of a Thermal Intergalactic Medium in the Coma Cluster

view Abstract Citations (19) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effect of Gaunt Factors on Analysis of X-Ray Spectra: Viability of a Thermal Intergalactic Medium in the Coma Cluster Margon, Bruce Abstract The effect of the choice of a Gaunt factor approximation on the analysis of the spectra of celestial X-ray sources is examined. It is found that the commonly used practice of setting the Gaunt factor to unity when comparing data with theoretical thermal-bremsstrahlung spectra leads to unacceptably large errors. The Born-approximation Gaunt factor yields satisfactory results in energy regimes applicable to current instrumentation. When an appropriate Gaunt factor is applied to the analysis of Uhuru data on the extended X-ray source in the Coma cluster of galaxies, the resulting best-fit temperature of kT = 12 (+ 12, -4) keV implies a velocity dispersion which agrees with that expected for a gas of the observed radius of the X-ray source in the known potential of the cluster. Thus, current X-ray data permit the existence of a velocity-supported thermal intergalactic medium in Coma. Subject headings: galaxies, clusters of - spectra, X-ray - intergalactic medium Publication: The Astrophysical Journal Pub Date: September 1973 DOI: 10.1086/152331 Bibcode: 1973ApJ...184..323M full text sources ADS | data products NED (1)