Radial Velocities Of Stars Research Articles

Quasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD 168112 (O5.5III(f$\mathsf{^+}$))

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f + )). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decrease of the X-ray flux of ∼30%. The radio emission on the other hand increases by a factor 5-7 between the two observations obtained roughly simultaneously with the XMM-Newton pointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT ∼ 2-3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD 168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD 168112 is indeed a binary, it must be seen under a fairly low inclination.

A photometric-spectroscopic analysis and the evolutionary status of the Algol-type binary U Coronae Borealis

The prime purposes of this study are to obtain reliable orbital parameters for the Algol-type binary U Coronae Borealis (U CrB) and to explain the evolutionary status of this system. All observations of the primary star's radial velocity are consistent with the value K 1 = 58.6 ′ 2.0 km s - 1 . Measurements ofthe radial velocity of the secondary component give K 2 = 185.2 ′ 5.0 km s - 1 Using the photometrically determined inclination of 78.7 ′ 0.3, the masses of the two stars are therefore deduced to be 4.74 ′ 0.28 and 1.46 ′ 0.06 M O . for the primary and secondary components, respectively. Using all available observations, we discuss the origin and evolution of the close binary system U CrB. We derive the restrictions concerning masses and period from a general network of calculations of medium mass close binary evolution. Detailed models are calculated within the derived ranges, giving the most likely initial system parameters as 4.5 M O . + 2.7 M O . and P i = 1.4 d. It turns out that the interactive evolution up to the present stage has been non-conservative. During its evolution, U CrB has lost about 14 per cent of its initial total mass (ΔM ∼ 1 M O .) and around 18 per cent of its initial total angular momentum. We also examine the possibility of probing dynamo action in the mass-losing component of U CrB. We point out that, in order to maintain the evolution of U CrB in its later stages, which is presumably driven by stellar 'magnetic braking', an efficient mechanism for producing large-scale surface magnetic fields in the donor star is required. We suggest that observed X-ray activity in U CrB may be a good indicator of its evolutionary status and the internal structure of the mass-losing component.

Radial velocities of early-type stars in the Perseus OB2 association

We present radial velocities for 29 B- and A-type stars in the field of the nearby association Perseus OB2. The velocities are derived from spectra obtained with AURELIE, via cross correlation with radial velocity standards matched as closely as possible in spectral type. The resulting accuracy is ~2 - 3 km s$^{-1}$. We use these measurements, together with published values for a few other early-type stars, to study membership of the association. The mean radial velocity (and measured velocity dispersion) of Per OB2 is 23.5 \pm 3.9 km s$^{-1}$, and lies ~15 km s$^{-1}$ away from the mean velocity of the local disk field stars. We identify a number of interlopers in the list of possible late-B- and A-type members which was based on Hipparcos parallaxes and proper motions, and discuss the colour-magnitude diagram of the association.

An extrasolar planet that transits the disk of its parent star.

Planets orbiting other stars could in principle be found through the periodic dimming of starlight as a planet moves across--or 'transits'--the line of sight between the observer and the star. Depending on the size of the planet relative to the star, the dimming could reach a few per cent of the apparent brightness of the star. Despite many searches, no transiting planet has been discovered in this way; the one known transiting planet--HD209458b--was first discovered using precise measurements of the parent star's radial velocity and only subsequently detected photometrically. Here we report radial velocity measurements of the star OGLE-TR-56, which was previously found to exhibit a 1.2-day transit-like light curve in a survey looking for gravitational microlensing events. The velocity changes that we detect correlate with the light curve, from which we conclude that they are probably induced by an object of around 0.9 Jupiter masses in an orbit only 0.023 au from its star. We estimate the planetary radius to be around 1.3 Jupiter radii and its density to be about 0.5 g x cm(-3). This object is hotter than any known planet (approximately 1,900 K), but is still stable against long-term evaporation or tidal disruption.

The dynamics of the nebula M1-67 around the run-away Wolf-Rayet star WR 124

A new point of view on the dynamics of the circumstellar nebula M1-67 around the run-away Wolf-Rayet (WR) star WR 124 is presented. We simulated the outbursts of nebulae with different morphologies, to compare the results to the observed dynamical spectra of M1-67. We found that it has been interacting with the surrounding ISM and has formed a bow shock due to its high velocity of about 180 kms −1 relative to the local ISM. The star is about 1.3 parsec away from the front of this bow shock. The outbursts that are responsible for the nebula are assumed to be discrete outbursts that occurred inside this bow shock. The ejecta collide with this bow shock shortly after the outburst. After the collision, they are dragged away by the pressure of the ISM, along the surface of the bow shock. The bow shock is oriented in such way that we are looking from the rear into this paraboloid, almost along the main axis. Evidence for this is given firstly by the fact that the far hemisphere is much brighter than the near hemisphere, secondly by the fact that there is hardly any emission found with radial velocities higher than the star's radial velocity, thirdly by the fact that the star looks to be in the centre of the nebula, as seen from Earth, and finally by the asymmetric overall velocity distribution of the nebula, which indicates higher radial velocities in the centre of the nebula, and lower velocities near the edges. We find evidence for at least two discrete outbursts that occurred inside this bow shock. For these outbursts, we find expansion velocities of vexp ≈ 150 kms −1 and dynamical timescales of about 0.8 and 2 ×10 4 yr, which are typical values for LBV outbursts. We therefore conclude that M1-67 originates from several outbursts that occurred inside the bow shock around WR 124, during an LBV phase that preceded the current WR phase of the star.

Rotational Broadening Measurement for the Neutron Star X‐Ray Transient XTE J2123−058

We used optical spectroscopy of the neutron star X-ray transient XTE J2123-058 to measure the rotational broadening of the binary companion's stellar absorption lines and determined that the companion's projected rotational velocity is v sin i = 121 km s-1. This value is considerably larger than the measurements of v sin i obtained previously for three other neutron star systems, where the values were between 34 and 65 km s-1. The larger value is likely due to the combination of high binary inclination and short (6 hr) orbital period for XTE J2123-058. Along with previously measured parameters, the rotational broadening measurement allowed us to determine the binary parameters, including the ratio of the neutron star mass to the companion mass, q = M1/M2 = 2.7, the neutron star mass M1 = 1.46 M☉, and the companion mass M2 = 0.53 M☉, assuming a Roche lobe-filling companion synchronously rotating with the binary orbit. These values are consistent with a previous measurement in which the Hα emission line was used to determine the semiamplitude of the neutron star's radial velocity curve (K1). It is a significant result that the two methods give consistent values. We also report the first measurement of the XTE J2123-058 companion's radius. Assuming synchronous rotation, we obtain R2 = 0.62 R☉, which is in line with that expected for a late K-type star on or close to the main sequence. Finally, we report the first precise spectroscopic determination of the binary orbital period (Porb = 21,442.3 ± 1.8 s).

Mapping the Galactic Halo. V. Sagittarius Dwarf Spheroidal Tidal Debris 60° from the Main Body

As part of the Spaghetti Project Survey, we have detected a concentration of giant stars well above expectations for a smooth halo model. The position (l ~ 350°, b ~ 50°) and distance (~50 kpc) of this concentration match those of the northern overdensity detected by the Sloan Digital Sky Survey. We find additional evidence for structure at ~80 kpc in the same direction. We present radial velocities for many of these stars, including the first published results from the 6.5 m Magellan telescope. The radial velocities for stars in these structures are in excellent agreement with models of the dynamical evolution of the Sagittarius dwarf tidal debris, whose center is 60° away. The metallicity of stars in these streams is lower than that of the main body of the Sgr dwarf, which may indicate a radial metallicity gradient prior to disruption.

The Proper Motion, Parallax, and Origin of the Isolated Neutron Star RX J185635−3754

The isolated neutron star RX J185635-3754 is the closest known neutron star to the Sun. Based on HST WFPC2 obervations over a 3 year baseline, I report its proper motion (332 +/- 1 mas/yr at a position angle of 100.3 +/- 0.1 degrees) and parallax (16.5 +/- 2.3 mas; 61 pc). This proper motion brings the neutron star from the general vicinity of the Sco-Cen OB association. For an assumed neutron star radial velocity between -55 and -60 km/s, the runaway O star zeta Oph, the Upper Sco OB association, and the neutron star come into spatial coincidence between 0.9 and 1.0 million years ago. RX J185635-3754 may be the remnant of the original primary of the zeta Oph system. If so, the space velocity suggests that the neutron star received a kick of about 200 km/s at birth.

The Central Dark Mass of the Milky Way

Measurements of the proper motions and radial velocities of stars in the central cluster of the Milky Way have revealed the presence of a 2-3 million solar mass black hole at the position of the compact radio source Sagittarius A* (SgrA*). The overall stellar motions do not deviate strongly from isotropy and are consistent with a spherical isothermal stellar cluster. Speckle spectroscopy with SHARP at the NTT and slit spectroscopy with ISAAC at the VLT suggests that several of them are early type stars. This is consistent with the idea that these stars are members of an early type cluster with small angular momentum and therefore are now in the immediate vicinity of SgrA*. Most recent data now allows to measure the curvatures of the stellar orbits for a few of the stars that are closest to the center and have the largest proper motions of up to 1400 km/s. The curvatures indicate that the stars indeed orbit the central compact object and will allow to further determine its mass and compactness.

Détermination des rayons de Céphéides

We present radial velocity data for 22 galactic Cepheid stars obtained with Coravel spectrometer. Continuous observation over several years has enabled us to obtain 852 individual velocities covering all the phases of the pulsation. The mean number of measurements per star is 39, ranging from 20 to 113. For each star radial velocity versus phase diagrams have been fitted by analytical relation, and the stellar radius variation has been derived by integration of this relation over the whole period. Using recent ubv photometry of the literature and velocity curves, we have calculated the radii of the stars using a method based on the Baade-Wesselink concept. For these 22 Cepheids we give a linear logarithmic period-radius relation with a range of 2,4 to 45 days.

Radial Velocities of Giant Stars in Globular Clusters11The WIYN Observatory is a joint facility of the University of Wisconsin—Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.

ABSTRACTWe report radial velocities for 303 giant stars in the globular clusters M3, M13, M15, and M92. Spectra were obtained using the 4 m Mayall and 3.5 m WIYN telescopes and the Hydra fiber positioner between 1993 and 1997; most spectra were provided by the NOAO WIYN Queue Program. Observations spanned times from a few days to several months. The uncertainties in the velocity measurements are typically 1 km s−1 or less. Several stars show velocity variations which may result from binary companions or atmospheric motions. Mean cluster velocities were measured to be −147.0 ± 0.3, −245.5 ± 1.0, −106.2 ± 0.3, and −120.3 ± 0.3 km s−1, for M3, M13, M15, and M92, respectively. Radial velocity observations for the photometric variable V73 (vZ 1406) in M3 confirm that the star varies with a period of 0.67 days.

New OB-association in Pup — CMa

A new method of determination of distances to stellar associations is proposed. This method is based on the measurements of mean thicknesses of globules of the systems of dark globules connected with that association. It is shown that the method is in good agreement with other known methods. A new grouping of OB stars in Pup-CMa is found. It is shown that this grouping has properties characteristic for OB-associations: the stars of that grouping have similar distances, similar radial velocities, the grouping is connected with molecular clouds, with Herbig-Haro objects, and cometary nebulae. All these results are in favour of this grouping to be a new OB-association. We named that association OB-association Pup-CMa. The preliminary results of12CO observations of molecular clouds connected with that association are also given. The radial velocities of these clouds are in good agreement with the mean radial velocity of stars in the association in Pup-CMa.

Using the Radial Velocity Spectrometer at the Dominion Astrophysical Observatory

AbstractTwo observing runs have been undertaken at the Dominion Astrophysical Observatory (DAO) using the radial velocity spectrometer (RVS). About 800 observations have been performed with both the K and F masks. All cross-correlation profiles have been divided by the corresponding flux monitor records and full gaussian functions have been fitted in order to determine the profile centers. A number of IAU standard radial velocity stars have been observed, with a typical internal precision for a given star of about 100 m s−1, which is a factor of two or three better than the usually adopted value for the RVS. Zero-point offsets between these observations and the standard values were also investigated.

Radial velocities of southern stars obtained with the photoelectric scanner coravel, VIII. Observations of 471 giant stars in omega centauri.

Radial velocities of southern stars obtained with the photoelectric scanner coravel, VIII. Observations of 471 giant stars in omega centauri.

Compact Radio Cores in the Galactic Center and Elsewhere

AbstractCompact radio cores are not only common in radio galaxies and quasars but also in many nearby galaxies with low-active, supermassive black holes. One famous example is the Galactic Center source Sgr A*. Recent studies of proper motions and radial velocities of stars in the inner parsec of the Galaxy convincingly demonstrate the presence of a compact dark mass of 2.5 · 106M⊙in the nucleus of the Milky Way. Millimeter VLBI and submm observations of Sgr A*thus probe a region of only a few Schwarzschild radii in diameter. In this paper I will review our current theoretical and observational knowledge of this source and compare it to some famous LINER galaxies like NGC 4258, NGC 3079, and NGC 6500. In all cases these radio cores can be well explained by a standard AGN jet model, and, with the exception of Sgr A*, large scale outflows are observed that have powers comparable to those inferred from the radio cores. Recent VLBI observations of radio-weak quasars and HST observations of Seyfert galaxies indicate that these AGN also produce powerful jets which, however, have relatively less luminous radio cores than radio-loud quasars and the LINERs discussed here. Therefore, jets and compact radio cores appear to be natural constituents of an AGN, but the reason why apparently some jets are radio-loud and others not remains a mystery.

The Masses and Radii of the Eclipsing Binary F Aurigae

We present a full determination of the fundamental stellar and orbital parameters of the eclipsing binary ζ Aurigae (K4 Ib + B5 V) using recent observations with the Hubble Space Telescope Goddard High Resolution Spectrograph (GHRS) and the Mark III long-baseline optical interferometer. The information obtained from spectroscopic and interferometric measurements is complementary, and the combination permits a complete determination of the stellar masses, the absolute semimajor axis of the orbit, and the distance. A complete solution requires that both components be visible spectroscopically, and this has always been difficult for the ζ Aur systems. The ζ Aur K star primary presents no difficulty, and accurate radial velocities are readily obtainable in the optical. However, the B star secondary is more problematic. Ground-based radial velocity measurements are hampered by the difficulty of working with the composite spectrum in the blue-violet region, the small number of suitable lines in the generally featureless optical spectrum of the B star, and the great width of the few available lines (the Balmer lines of hydrogen and a few weak He I lines) due to rapid rotation. We avoid the worst of these problems by using GHRS observations in the ultraviolet, where the K star Flux is negligible and the intrinsic B star spectrum is more distinctive, and obtain the most accurate determination of the B star radial velocity amplitude to date. We also analyze published photometry of previous eclipses and near-eclipse phases of ζ Aur in order to obtain eclipse durations, which fix the length of the eclipse chord and therefore determine the orbit inclination. The long-baseline interferometry (LBI) yields, in conjunction with the spectroscopic solution, the distance to the system and thus the absolute stellar radius of the resolved K supergiant primary star, ζ Aur A. The secondary is not resolved by LBI, but its angular (and absolute) radius is found by Fitting the model stellar flux plus an interstellar extinction model to the flux-calibrated GHRS data. We Find MK = 5.8 ± 0.2 M☉, MB = 4.8 ± 0.2 M☉, RK = 148 ± 3 R☉ and RB = 4.5 ± 0.3 RB for the masses and radii of the ζ Aur stars. We determine the distance to ζ Aur to be 261 ± 3 pc. Additionally, we refine the stellar parameters of the B star secondary presented in the 1995 spectroscopic study of Bennett, Brown, & Linsky. We also determine the effective temperature of the K star primary using values of the bolometric flux, angular diameter, and interstellar extinction derived in this study. The positions of the ζ Aur stars on the theoretical H-R diagram are compared to current evolutionary model tracks, and the resulting good agreement provides a strong check of the internal self-consistency of this analysis and the accuracy of the theoretical models. The ζ Aurigae stars are confirmed to be coeval with an age of 80 ± 15 Myr.

THE MASS RATIO AND THE DISK IMAGE OF THE X-RAY NOVA GS 2000+25

ABSTRACT Keck observations of the black hole candidate GS 2000+25 in quiescence have recently been used by Filippenko, Matheson, and Barth to determine a mass function f(Mx) = 4.97 ± 0.10 solar mass for the compact object. Our reanalysis of the data confirms this result (5.01 ± 0.12 solar mass). We estimate a mass ratio of q = Mc/Mx = 0.042 ± 0.012 from the rotational broadening of the companion star, v sin i = 86 ± 8 km s-1. From q and the companion star's radial velocity Kc, we derive the mass of the compact object Mx = (5.44 ± 0.15) sin-3 i solar mass and the mass of the companion star Mc = (0.23 ± 0.02) sin-3 i solar mass. Constraints on the inclination (75 degrees > i > 47 degrees) lead to 6.04 < Mx < 13.9 and 0.26 < Mc < 0.59 (1-sigma) in solar mass units. We determine a spectral type of K3-K6 for the companion star, which contributes more than 72% of the light at red wavelengths (94% ± 5% for K5 V). Our analysis shows that the companion is an undermassive star, slightly evolved but not a subgiant. Consistent with the work of Filippenko et al. we detect Li I lambda-6708 absorption (equivalent width 150 ± 85 mA) in the spectrum of the companion. A Doppler image of the system shows evidence for a bright spot which contributes 10% of the emission-line flux density, and arises in the range 0.3-0.6 RL1 of the accretion disk, where L1 is the inner Lagrangian point. Along the trajectory of the gas stream, the velocities are initially ballistic and gradually become Keplerian.

Dynamics of the Galactic Globular Cluster NGC 3201

B,V CCD frames have been used to derive surface brightness profiles for NGC 3201 out to ~18 arcmin. A total of 857 radial velocities with median precision ~1 km/s for 399 member giants have been used to trace the velocity dispersion profile out to 32' (the approximate tidal radius from fits of single-mass, isotropic King-Michie models to the cluster surface brightness profiles). The median difference in radial velocity for stars on either side of an imaginary axis moved through the cluster in 1 degree steps shows a significant maximum amplitude of 1.22+/-0.25 km/s. We discuss possible explanations of this result, including: (1) cluster rotation; (2) preferential stripping of stars on prograde orbits near the limiting radius; (3) the projection of the cluster space velocity onto the plane of the sky and (4) a slight drift in the velocity zero point. It is difficult to identify the primary cause of the observed velocity field structure unambiguously, and we suspect that all of the above processes may play a role. The B,V surface brightness profiles and radial velocities have been modeled with single- & multi-mass King-Michie models and nonparametric techniques. The density and M/L profiles show good agreement over 1.5<R<10 pc, and both approaches suggest a steady rise in M/L with distance from the cluster center. Due to the low cluster luminosity, we are unable to place useful constraints on the anisotropy of the velocity dispersion profile, though the global mass-to-light ratio is well-constrained by the models as ~2.0 +/-0.2 for the multi-mass and nonparametric models, compared to ~ 1.65 +/-0.15 for models having equal-mass stars. Our best-fit, multi-mass models have mass function slopes of x~0.75 +/-0.25, consistent with findings that mass function depends on the position relative to the potential of the Galaxy.

A Jupiter-mass companion to a solar-type star

The presence of a Jupiter-mass companion to the star 51 Pegasi is inferred from observations of periodic variations in the star's radial velocity. The companion lies only about eight million kilometres from the star, which would be well inside the orbit of Mercury in our Solar System. This object might be a gas-giant planet that has migrated to this location through orbital evolution, or from the radiative stripping of a brown dwarf.

Radial velocities of stars in the globular cluster M4 and the cluster distance

The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km/s and a rederivation of existing proper motions. The mean radial velocity of the cluster is 70.9 +/- 0.6 km/s. The velocity dispersion is 3.5 +/- 0.3 km/s at the core, dropping marginally towards the outskirts. Such a low internal dispersion is somewhat at odds with the cluster's orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruption is high; a tidal radius two-thirds the currently accepted value would eliminate the discrepancy. The cluster mass-to-light ratio is also small, M/L(sub V) = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a cluster of moderate and concentration with a mass-to-light ratio among the lowest known. The astrometric distance to the cluster is also smaller than expected, 1.72 +/- 0.14 kpc. This is only consistent with conventional estimates of the luminosity of horizontal branch stars provided an extinction law R = A(sub V)/E(B-V) approximately 4 is adopted, as has been suggested recently by several authors.