Apparent Radial Velocity Research Articles

Emission from the Secondary Star in the Old Cataclysmic Variable WZ Sagittae

We present the first detection of the mass donor star in the cataclysmic variable WZ Sagittae. Phase-resolved spectroscopy reveals narrow Balmer emission components from the irradiated secondary star during the 2001 outburst. Its radial velocity curve indicates a systemic velocity of -72 ± 3 km s-1 and an apparent velocity amplitude of K = 493 ± 10 km s-1. Doppler tomography reveals a highly asymmetric accretion disk including a significant bright spot contribution 20 days into the outburst. We estimate the apparent primary radial velocity using the Hα tomogram and find K = 37 ± 5 km s-1. Accounting for the likely systematic errors affecting both K1 and K2 measurements, we conservatively derive 493 km s-1 0.70 M☉ and a low-mass secondary with M2 < 0.11 M☉. A nondegenerate mass donor, implying WZ Sge has not yet evolved through its minimum period, is therefore not ruled out by our observations. This would require an improved estimate of K1.

The Value of Fabry-Perot Interferometry in Studying Long-Term Convective Line Shifts

AbstractSmall &lt; 10 m s−1 variations of radial velocity (RV) with multi-year periods in solar-type stars may be indistinguishable from the effects induced on lines by stellar activity cycles (Dravins 1985; Saar &amp; Donahue 1997). Dravins (1992) recommended a resolving power R &gt; 3 × 105 to measure accurately the subtle changes in the shapes of bisectors of photospheric absorption lines driven by changes of granular convection in slowly rotating dwarf stars. Butler et al. (1996) measure impressively small amplitudes of RVs by using echelle spectrographs that cover a broad spectrum. However, to cover a broad spectrum the resolving power is typically limited to &lt; 7 × 104, and the necessary presence of the iodine absorption spectrum may make it difficult to measure convective line shifts contemporaneously with the RV time series. Furthermore, to reach an RV accuracy of ± 3 ms−1 the whole profile of each line is used, thus maximizing the possibility that changes in the shapes of the lines’ C-bisectors could induce an apparent variation of RV.Dravins (1985) recommended the exclusive use of the steep flanks of photospheric absorption lines to minimize the effects of convection on apparent RV. McMillan et al. (1993, 1994) demonstrated that such RV measurements made with a Fabry-Perot etalon (FPE) interferometer in transmission can be stable in the presence of stellar line variations seen by other investigators whose measurements were not based exclusively on line flanks. Dravins also prescribed high resolving power, high signal-to-noise ratio, high instrumental contrast, and low instrumental wings to analyze the rest of the line profile for convectively-driven changes (Dravins 1978, 1987, 1992). A double- or multiple-pass FPE scanning whole line profiles can provide high R, high contrast, low wings, and a stable, symmetrical line spread function with small (portable) optics, although the low photon efficiency will restrict its use to a few carefully selected stars. The spectral classes of these stars should span the spectral classes of the stars being monitored by others for planets. We describe a possible implementation of this concept that has the potential for adequate photon flux: observing symbiotically through another instrument on a 6-m to 10-m class telescope.

Astrometric versus Spectroscopic Radial Velocities

AbstractThe apparent radial velocity of a star, as deduced from wavelength shifts, comprises not merely its true velocity, but also components arising from dynamics in the star’s atmosphere, gravitational redshift, and other effects. For the Sun, such phenomena can be segregated since the relative Sun-Earth motion is known from planetary system dynamics. This is now becoming possible also for other stars, whose true radial motions are determined through space astrometry. A study of the differences between accurate astrometric velocities (from Hipparcos), and precise spectroscopic values (from ELODIE) is in progress. Data for cool stars in the Hyades indicate a tendency of relative blueshifts among earlier main-sequence F-type stars, and in giants. This is theoretically expected: an increased convective blueshift due to the more vigorous convection in F-stars, and a decreased gravitational redshift in giants.

Measuring the Rotation Speed of Giant Stars from Gravitational Microlensing

During some gravitational lensing events, the lens transits the face of the star. This causes a shift in the apparent radial velocity of the star which is proportional to its rotation speed. It also changes the magnification relative to what would be expected for a point source. By measuring both effects, one can determine the rotation parameter $v\sin i$. The method is especially useful for K giant stars because these have turbulent velocities that are typically large compared with their rotation speed. By making a series of radial velocity measurements, one can typically determine $v\sin i$ to the same accuracy as the individual radial velocity measurements. There are approximately 10 microlensing transit events per year which would be suitable to make these measurements.

A spectroscopic and photometric study of FK Comae in 1989

Results of an observational campaign, coordinated between visual photometry, optical spectroscopy, and UV spectroscopy, to elucidate the characteristics of FK Comae are presented. The photometry showed complicated but systematic behavior. Photospheric absorption lines were distorted by a Doppler-shifted bump caused by dark starspots resulting in small apparent radial velocity variations. No radial velocity variations characteristic of orbital motion were seen to a level of 3 km/s. Broad emission in H-alpha was modulated at the photospheric rotational amplitude, implying an origin no farther from the rotational axis than 1 stellar radius. The strengths of Ca II lines are modulated in phase with H-alpha but do not have velocity-modulated wings like H-alpha.

Relation between the bed structure and the apparent radial gas velocity profile at the bed outlet in tubular apparatus

The effects of the bed structure on the apparent radial gas velocity distribution at the outlet of the bed packed in a tube were investigated experimentally. The experiments revealed that the effects depend on the static pressure distribution along the bed. When the flow resistance within the bottom inlet zone is larger than that within the upper zone, for example, on account of the difference in the bed porosity or the geometry of the bed elements, the effects of the bottom zone increase. It can also be observed that the maximal length of the zone of the gas inlet effects corresponds to 80 diameters of the bed elements, and approaches strongly a practically constant length of 15–20 diameters, as the ratio of the gas pressure drop in the packed segment of the tube to that in its empty part of the same length increases to a value of about 2 × 10 3.

The velocity field of a coronal mass ejection: The event of September 1, 1980

A coronal mass ejection with the appearance of two sets of overlapping loops occurred at about 0600 UT on September 1, 1980, over the northwest limb of the sun. It was one of the fastest events observed by the Solar Maximum Mission coronagraph during the 1980 epoch, with apparent radial velocity components of several features approaching 1000 km s−1. A study of the slow evolution of Hα prominence filaments and coronal structures in the northwest solar sector suggests that the mass ejection resulted from the disruption of a helmet streamer in association with, possibly, two filaments to give rise to the double‐loop structure. This event is well covered by 10 coronagraph images of good quality so that the complex velocity field, defined by the apparent motions of many different parts of the mass ejection, can be mapped out as a function of space and time. The results of such an analysis are presented and related to current concerns in the theoretical understanding of mass ejections. In particular, it is concluded that a self‐similar description of the velocity field is a gross oversimplification and that although some evidence of wave propagation can be found, the bright features in this mass ejection are plasma structures moving (presumably) with frozen‐in magnetic fields, rather than waves propagating through plasmas and magnetic fields.

Spectrophotometry of an X-ray source near M33

view Abstract Citations (10) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometry pf an X-ray source near M33 Christian, C. A. ; Schommer, R. A. Abstract IIDS spectrophotometry of an object identified with the X-ray source near M33 observed by Long et al. (1981) have been obtained. The source has an apparent radial velocity of 10,800 + or - 800 km/sec, an integrated spectral type similar to a late G or early K giant, and an optical image with noticeably elongated isophotes, suggesting that the source is an elliptical galaxy at z = 0.03 rather than a globular cluster. Publication: The Astrophysical Journal Pub Date: February 1982 DOI: 10.1086/183727 Bibcode: 1982ApJ...253L..13C Keywords: Astronomical Spectroscopy; Spectrophotometry; Spiral Galaxies; X Ray Sources; Globular Clusters; Image Dissector Tubes; Radial Velocity; Astrophysics full text sources ADS | data products SIMBAD (5) NED (3)

Microwave Water Vapor Emmision from Galactic Sources

view Abstract Citations (112) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Microwave Water Vapor Emission from Galactic Sources Sullivan, Woodruff T., III Abstract Water vapor emission arising from the 1.35-cm 616 523 transition has been observed from the galactic sources W3-OH, Ori A, VY CMa, NGC 6334(N), Sgr B2, W49, W51, ON 1, and W75(S) in nine distinct periods extending from 1969 January to 1970 June. We have used both the 85-foot (26-meter) antenna of the Naval Research Laboratory and the 140-foot (43-meter) antenna of the National Radio Astronomy Observatory. Remarkable changes have occurred in the intensity, width, apparent radial velocity, and linear polarization of the individual H2O features. For each source we summarize its properties, describe the H2O variations, and present time sequences of the profiles as well as diagrams showing the behavior of individual features with time. Typical time scales for these changes range from several months to only a few days. No system or periodicity has been found in these variations. Assuming that the emission is due to a maser mechanism, the variations are most likely due to changes in the pump power or in the maser geometry. In an appendix we develop the equation of radiative transfer for a saturated maser. Observational and theoretical constraints on the seven free parameters of our model of an H2O maser are given. The degree of saturation and physical conditions must vary greatly from feature to feature. We propose that the masers occur in zones on the edge of dust clouds. Gaseous H2O is created by evaporation and sputtering off icy dust grains, but is then photodissociated on a time scale of months by the radiation from a nearby 0 or early B star. The extreme variability of the profiles is then mainly a consequence of the continually evolving geometry of the H2O zone. These zones may be associated with the bright rim structures often found at the edge of dust clouds in H II regions. Publication: The Astrophysical Journal Supplement Series Pub Date: May 1973 DOI: 10.1086/190273 Bibcode: 1973ApJS...25..393S Keywords: masers; molecules; interstellar; nebulae; interstellar matter; line formation; Orion Nebula; radio lines full text sources ADS | data products SIMBAD (18) NED (1)

Variations in Frequency and Intensity of 1.35-CENTIMETER H_{2}O Emission Profiles in Galactic H II Regions

view Abstract Citations (44) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Variations in Frequency and Intensity of 1.35-CENTIMETER H_{2}O Emission Profiles in Galactic H II Regions Sullivan, Woodruff T., III Abstract We report observations of 1.35-cm 6is "523 H2O emission in the galactic sources W3, Ori A, and W49 over the period 1969 January to 1970 June. Remarkable changes have occurred in the complex frequency structure of the line profiles and in the intensity, width, apparent radial velocity, and polarization of the individual features. Each of the features contributing to an HiO profile arises from a separate dense region able to sustain maser emission and associated with an H ii region. The changes in intensity and width of features are consistent with a partially saturated maser in a medium undergoing changes in pump power and gain of the maser. Hyperfine structure and blending of independently varying features can account for the apparent shifts in velocity. On one possible model a typical maser has a gain 10 ", kinetic temperature 500" K, dimensions 1 X 1 X 100 a.u., and H2O density 5 X 10 . The degree of saturation and physical conditions vary greatly, however, from feature to feature. Publication: The Astrophysical Journal Pub Date: June 1971 DOI: 10.1086/150961 Bibcode: 1971ApJ...166..321S full text sources ADS |