Luminosity Correlation Research Articles

Solar luminosity variations in solar cycle 21

The ACRIM I experiment (Active Cavity Radiometer Irradiance Monitor) on the solar maximum Mission (SMM) satellite has provided a nearly continuous record of solar total irradiance variations since early 19801. It has detected variations on time scales ranging from minutes to SMM's lifetime. The long-term variations have revealed a downward trend during the declining phase of solar cycle 21 (ref. 2) of the sunspot cycle, a flat period between mid-1985 and mid-1987, and an upturn in late 1987 which suggests a direct correlation of luminosity and solar active region population. If the upturn continues into the activity maximum of solar cycle 22, a relation between solar activity and luminosity of possible climatological significance could have been discovered. The sense of the correlation agrees with what has been predicted from the coincidence of the 'little ice age' climate anomaly in the sixteenth and seventeenth centuries and the Maunder Minimum of solar activity3. The best-fit relationship for the variation of total irradiance S, with sunspot number Rz, and 10–cm flux F10, are S=1,366.82+7.7l×10−3 Rz and S=1,366.27+8.98×10−3 F10 (W m−2). These could be used to approximate total irradiance variations over the periods for which these indices have been compiled.

X-ray time variability and luminosity correlations in BL lacertae objects

We present the preliminary results of a study of the soft X-ray properties of a sample of 34 BL Lacertae objects observed with the the EXOSAT Observatory. Strong correlations between the X-ray, optical and radio fluxes have been found in the subsample of X-ray selected objects. X-ray variability is common and has been significantly detected in 14 (8 × ray-selected and 6 radio-selected) out of the 25 objects observed more than once. Flux variations by up to a factor 5 have been found. The commonest form of variability encountered consists of small amplitude variations about a quiescent flux level whose mean value remains roughly constant over time scales of years.

A five-band study of spiral galaxies - X-ray, optical, near- and far-infrared, and radio continuum correlations

A statistical analysis is given of the relationships between global emission properties of spiral galaxies, including the radio continuum, far-infared, near-infrared H-band, optical (B), and X-ray emission. Different properties are observed in early-type and in late-type spiral galaxies, which can be ascribed to the presence of prominent bulges in the former. In late-type spirals, the statistical properties of the emission at different wavelengths are consistent with a common disk/arm origin. The power-law exponents of the correlations are consistent with a steeper IMF in low-luminosity galaxies and with the presence of an obscured starburst component in high-luminosity galaxies. The strongest correlation of the radio continuum luminosity with any other variable is with the far-infrared, suggesting that the radio emission is disjoint from the older low-mass stellar component.

X-ray, optical, and infrared luminosity correlations in radio-quiet quasars

view Abstract Citations (61) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-Ray, Optical, and Infrared Luminosity Correlations in Radio-quiet Quasars Kriss, Gerard A. Abstract For a sample of 88 radio-quiet quasars that includes 15 X-ray upper limits, I find that the X-ray and IR luminosities follow a significantly nonlinear relation (L_2keV_ ~ L^0.73^_1 micron_) that is consistent with that found for the X-ray and optical luminosities. The redshift dependence is weak and may be nonexistent. The shape of the optical through infrared continuum varies only slightly with luminosity. The most significant change is the lack of a strong ultraviolet bump in low luminosity objects with L_1 micron_ < 10^30^ ergs s^-1^ Hz^-1^. More luminous quasars have significantly stronger bumps, but above 10^30^ ergs s^-1^ Hz^-1^ the strength of the bump does not correlate with luminosity. The relatively constant shape of the infrared through optical continuum implies that a systematic change in the X-ray continuum of quasars with increasing luminosity produces the nonlinear relation between the X-ray luminosity and the optical and IR luminosities. Either the overall normalization of the X-ray continuum relative to the optical and IR must decrease, or the X-ray continuum must flatten with increasing luminosity, or the strength of a soft X-ray excess must decrease with increasing luminosity. Without detailed knowledge of the X-ray and infrared spectra as a function of luminosity, it is difficult to place significant constraints on emission mechanisms. Publication: The Astrophysical Journal Pub Date: January 1988 DOI: 10.1086/165940 Bibcode: 1988ApJ...324..809K Keywords: Infrared Spectra; Luminosity; Quasars; Visible Spectrum; X Ray Spectra; Accretion Disks; Black Holes (Astronomy); Continuous Spectra; Correlation; Radio Spectra; Red Shift; Astrophysics; INFRARED: SOURCES; QUASARS; RADIATION MECHANISMS; X-RAYS: SOURCES full text sources ADS | data products SIMBAD (85) NED (84)

Luminosity dependence in the ratio of X-ray to infrared emission of QSOs

view Abstract Citations (8) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Luminosity Dependence in the Ratio of X-Ray to Infrared Emission of QSOs Worrall, D. M. Abstract The correlation of X-ray and near-infrared luminosity is studied for a sample of radio-quiet QSOs. The X-ray to infrared ratio is found to decrease as the infrared luminosity increases. No preference is found between the correlations of X-ray luminosity with optical or infrared luminosity. This implies that optical and infrared emission are equally good predictors of X-ray emission. Source models which directly link infrared and X-ray emission are discussed, and a preference is found for a specific synchrotron self-Compton model. This model predicts the correct luminosity dependence of the X-ray to infrared ratio if certain conditions apply. Publication: The Astrophysical Journal Pub Date: July 1987 DOI: 10.1086/165360 Bibcode: 1987ApJ...318..188W Keywords: Infrared Spectra; Luminosity; Quasars; X Ray Spectra; Astronomical Models; Compton Effect; Near Infrared Radiation; Synchrotron Radiation; Visible Spectrum; Astrophysics; INFRARED: SOURCES; QUASARS; RADIATION MECHANISMS; X-RAYS: SOURCES full text sources ADS | data products SIMBAD (69) NED (64)

Beaming and the X-ray, optical and radio properties of quasars

We examine the correlations of X-ray and optical luminosities with radio properties for radio-selected quasars. A remarkably strong correlation is found to exist between the total radio luminosity (irrespective of whether it comes from a compact core or extended lobes) and the X-ray luminosity. A weaker correlation is found between the radio luminosity and the optical luminosity. The results are consistent with a two-component origin for the optical/X-ray emission, one isotropic and one relativistically beamed. This model also accounts for the change of slope with radio structure for the radio/X-ray luminosity correlation noted by Kembhavi et al. Quasars with flat radio spectra are found to have smaller emission-line equivalent widths than do steep-spectrum quasars, again in the sense predicted by the beaming hypothesis.

A 6 centimeter radio survey of short-period active binary stars

Thirteen binaries with periods in the range of 0.2-2.0 days have been observed at 6 cm wavelength with the VLA. Eight out of these thirteen systems were detected, of which seven are RS Canum Venaticorum systems and one is an Algol system, with observed fluxes in the range of 0.3-5.0 mJy. The individual characteristics of the detected sources are briefly discussed. As a group, relative to active binaries of longer orbital periods, the short-period active binaries have a slightly lower mean radio luminosity. There is also a clear correlation of high radio luminosity with high X-ray luminosity evident in these short-period systems, although a functional dependence cannot be determined from noncontemporary data.

Mass segregation and the rank correlation of luminosity with projected distance in clusters of galaxies

Mass segregation and the rank correlation of luminosity with projected distance in clusters of galaxies

Luminosity correlations in quasars

Simulations are conducted with and without flux thresholds in an investigation of quasar luminosity correlations by means of a Monte Carlo analysis, for various model distributions of quasars in X-rays and optical luminosity. For the case where the X-ray photons are primary, an anticorrelation between X-ray-to-optical luminosity ratio and optical luminosity arises as a natural consequence which resembles observations. The low optical luminosities of X-ray selected quasars can be understood as a consequence of the same effect, and similar conclusions may hold if the X-ray and optical luminosities are determined independently by a third parameter, although they do not hold if the optical photons are primary. The importance of such considerations is demonstrated through a reanalysis of the published X-ray-to-optical flux ratios for the 3CR sample.

Accretion powered X-ray pulsars

A unified description of the properties of 14 X-ray pulsars is presented and compared with the current theoretical understanding of these systems. The sample extends over six orders of magnitude in luminosity, with the only trend in the phase averaged spectra being that the lower luminosity systems appear to have less abrupt high energy cutoffs. There is no correlation of luminosity with power law index, high energy cutoff energy or iron line EW. Detailed pulse phase spectroscopy is given for five systems.

Einstein observations of cool stars

Observations of cool stars with the Einstein Observatory (HEAO-2) have brought about a fundamental change in our knowledge and understanding of stellar coronae. The existence of X-ray emission from stars throughout the H-R diagram, the wide range of X-ray luminosity within a given spectral and luminosity class, and the strong correlation of X-ray luminosity with stellar age and rotation are among the more significant Einstein results. These results are strong evidence for the influence of stellar dynamo action on the formation and heating of stellar coronae. A discussion of relevant consortium and guest observations will be given. The Hyades cluster, in particular, will serve as an example to demonstrate the usefulness of X-ray observations in the study of stellar activity and coronal evolution.

The distribution of mass in SC galaxies

view Abstract Citations (78) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The distribution of mass in SC galaxies Burstein, D. ; Rubin, V. C. ; Thonnard, N. ; Ford, W. K., Jr. Abstract For a sample of 21 Sc galaxies ranging from very low to very high luminosity, we have previously presented rotational velocities across ∼83% of the galaxy isophotal radius, R25. We now analyze the mass distributions for this same sample, and show that for all galaxies, the mass distribution has a single unique form, when the masses are each scaled by a mass scale length, Rm. Unlike luminosity scale lengths which are larger for more luminous (larger) galaxies, mass scale lengths are smaller for galaxies of high luminosity. As normalized here (the radius encompassing a mass of 1010 Msun), Rm is near 4 kpc for a low luminosity Sc and is near 1.5 kpc for a high luminosity Sc. A low luminosity Sc contains a single mass scale length, a high luminosity Sc contains many tens of scale lengths within its isophotal radius. At similar multiples of their scale lengths, all Sc's have equal interior masses. The form of the characteristic mass curve implies that rotation curves are still rising slightly at radii of many scale lengths, V ∝ r0.1 or r0.2, and local density falls off slower than 1/r2 (ρ ∝ r-1.7). We conclude that the rotational velocities remain high at large nuclear distances due to the presence of significant nonluminous mass at large radii. Correlations between integral mass, luminosity, mass scale length, isophotal radius, and velocity at the isophotal radius are determined and discussed. The correlation of luminosity with V(R25)) is as steep as that found in the infrared. The ratio of mass to luminosity interior to the isophotal radius is independent of luminosity and equals 3.0 ± 0.3 for Sc galaxies. Publication: The Astrophysical Journal Pub Date: February 1982 DOI: 10.1086/159611 Bibcode: 1982ApJ...253...70B Keywords: Galactic Rotation; Mass Distribution; Mass To Light Ratios; Spiral Galaxies; Astronomical Photometry; Galactic Radiation; Isophotes; Luminous Intensity; Stellar Mass; Astrophysics full text sources ADS | data products NED (20)

A confusion-limited extragalactic source survey at 4.755 GHz. III - Accurate positions and optical identifications

Accurate positions of sources stronger than 15 mJy at 4.755 GHz from a survey covering almost 0.01 sr of extragalactic sky were measured with the VLA. Optical identifications were made from the PSS prints on the basis of position coincidence alone. The spectral index ..cap alpha..(1.415,4.755) distributions of the identified QSO's and galaxies are significantly different from the corresponding distributions of strong-source identifications. The relative scarcity of faint flat-spectrum (..cap alpha.. 3) redshift, while the lack of faint galaxies with ..cap alpha..> or =+0.8 results from the spectral index--luminosity correlation of radio galaxies and the limited sensitivity of the PSS prints. The areal densities of optically selected and radio-selected QSO's brighter than m/sub b/ = +19.5 were compared, and both can be represented by a single, smoothly varying function of flux density.

The dynamics of binary galaxies

This paper presents a general analysis of dynamical models for scale-free ensembles of binary galaxies. Such models have constant but arbitrary orbital eccentricity and power-law relationships between pair separation and both number density and the scale of the relative velocity distribution. Their properties are easily simulated and analytic expressions are given both for the correction factors required to obtain unbiased estimates of the mean mass and mean mass-to-light ratio of a binary sample, and for the uncertainty in such estimates caused by sampling fluctuations and by observational errors. The practical application of these models is discussed, and appropriate methods are suggested for estimating the intrinsic density distribution, the pair interaction potential, the orbital eccentricity and a representative M/L ratio. A simple correction factor method of obtaining mean masses and mass-to-light ratios is shown to be subject to considerably less systematic error and to give more reliable results than apparently more sophisticated distribution fitting techniques. A reanalysis of Turner's (1976a) data sample illustrates the use of scale-free models, and brings to light a number of errors and inconsistencies in earlier work. The sample shows no evidence for intrinsic luminosity–separation correlations nor for any positive correlation of luminosity and M/L ratio; it gives at most only very weak evidence for predominantly circular rather than predominantly radial orbits. The mass-to-light ratio obtained by the correction factor method for Turner's primary data sample has a formal error equal to its nominal value. This situation can be remedied by the unbiased rejection of a few pairs which contribute heavily to the variance of the estimate. For such culled samples the derived M/L ratios have a 20 per cent uncertainty due to sampling fluctuations, compounded with a somewhat larger systematic uncertainty arising from poor knowledge of certain model parameters; they are a factor of 2 smaller than the values given by Turner (1976b). Monte Carlo simulations of the dynamics of Turner's sample are constructed on the hypotheses of Keplerian orbits and a dispersion-free relation between mass and luminosity. Such models agree well with the data if observational errors in the velocities are rather larger than those quoted by Turner.

The x-ray luminosity-redshift relationship of quasars

Chronometric cosmology provides an excellent fit for the phenomenological x-ray luminosity-redshift relationship for 49 quasars observed by the Einstein satellite. Analysis of the data on the basis of the Friedmann cosmology leads to a correlation of absolute x-ray luminosity with redshift of >0.8, which is increased to approximately 1 in the bright envelope. Although the trend might be ascribed a priori to an observational magnitude bias, it persists after nonparametric, maximum-likelihood removal of this bias.

An ultraviolet view of stellar winds

Ultraviolet observations of mass-loss effects in O stars have, over the past decade, revealed a broad picture of a phenomenon whose extent was only partially evident from earlier ground-based observations. Ultraviolet resonance lines of a variety of ionization stages of several common elements provide a comprehensive probe of the low-density, extended winds. Three general types of information have been derived from ultraviolet spectroscopy of mass-loss profiles: (1) the nature of the stars which experience mass loss via radiatively-driven winds; (2) the physical conditions in the winds; and (3) variability in the outflow, which in turn may yield clues to the origins of the winds. Observations and results in each of these areas are reviewed, and some new results are included. A good correlation of mass loss rate and luminosity is indicated by the data, in agreement with theoretical predictions. Time variations in the P Cygni profiles may be quite common, with variability on times of hours or longer. Anticipated new observations, which should be possible with existing and planned instrumentation, are described.

The correlation of mass outflow velocity and luminosity for Mira variables

view Abstract Citations (14) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The correlation of mass outflow velocity and luminosity for Mira variables. Cahn, J. H. ; Wyatt, S. P. Abstract Available data on the terminal expansion velocities of circumstellar shells around Mira variables are examined which are derivable from SiO, OH, and CO radio line profiles. It is found that the terminal expansion velocities are positively correlated with the mean bolometric luminosities of the central stars. In an attempt to account for the interdependence of these parameters, simple hydrodynamical calculations are carried out concerning the gas outflow close to a Mira and the coupled outflow of gas and dust grains beyond the radius where the grains originate. The results suggest that the interaction of grains, gas, and stellar radiation pressure is responsible for the correlation and that the gas is accelerated to final velocities somewhat less than 5 km/s for less luminous Miras and in excess of 20 km/s for more luminous Miras. The observed dependence and the calculations are shown to require that the more luminous Miras produce somewhat larger grains than the less luminous ones. Publication: The Astrophysical Journal Pub Date: September 1978 DOI: 10.1086/182764 Bibcode: 1978ApJ...224L..79C Keywords: Binary Stars; M Stars; Mira Variables; Stellar Envelopes; Stellar Mass Ejection; Variable Stars; B Stars; Bolometers; Gas Flow; Stellar Luminosity; Stellar Winds; Astrophysics; Circumstellar Shells:Mira Variables; Luminosities:Mira Variables; Mass Loss:Mira Variables full text sources ADS |

New silicon monoxide masers

Seven Mira variable stars with silicon monoxide maser emission have been found. All are later than M4 and heavily reddened. Two were observed near maximum light. One, Y Cas, seems to bear out the correlation of 43-GHz SiO maser luminosity and mean spectral type at maximum light. RT Aql, however, falls about 1 mag below the expected brightness. A catalog of SiO maser stars is given.

X-ray clusters of galaxies - Correlation of X-ray luminosity with galactic content

All 14 X-ray clusters of galaxies detected by the Ariel 5 satellite at high galactic latitudes with redshifts of less than 0.05 are analyzed optically for galaxy content. A strong correlation is found between cluster X-ray luminosity and galaxy type: the fraction of spiral galaxies in a cluster decreases rapidly with increasing X-ray luminosity. The observed correlation is consistent with a combined model of thermal bremsstrahlung emission from a hot intracluster gas and stripping of the spiral galaxies caused by the ram pressure of the same intracluster gas.

The origin of X-ray sources in clusters of galaxies

view Abstract Citations (18) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The origin of X-ray sources in clusters of galaxies. Katz, J. I. Abstract It is suggested that the extended X-ray sources in clusters of galaxies may be explained by a population of compact sources, like those known in our own Galaxy. To test this hypothesis a simple model for the X-ray luminosity to mass ratio is proposed, and a correlation of the X-ray luminosity with the virial mass is sought. The results are inconclusive. Other possible tests are discussed. Publication: The Astrophysical Journal Pub Date: July 1976 DOI: 10.1086/154462 Bibcode: 1976ApJ...207...25K Keywords: Astronomical Models; Galactic Clusters; Luminous Intensity; X Ray Sources; Correlation; Heao; Milky Way Galaxy; Star Distribution; Astrophysics full text sources ADS |