Radial Velocity Modulation Research Articles

Photospheric and chromospheric activity on the young solar-type star HD 171488 (V889 Herculis)

We present the results of contemporaneous spectroscopic and photometric monitoring of the young solar-type star HD171488 (Prot~1.337 d) aimed at studying surface inhomogeneities at photospheric/chromospheric levels. Echelle FOCES spectra (R~40000) and Johnson photometry have been performed in 2006. Spectral type, rotational velocity, metallicity, and gravity were determined using a code developed by us. The metallicity was measured from the analysis of iron lines. The spectral subtraction technique was applied to the most relevant chromospheric diagnostics included in the FOCES spectral range (CaII IRT, Halpha, HeI-D3, Hbeta, CaII H&K). A model with two large high-latitude spots is sufficient to reproduce the B/V light curves and the radial velocity modulation, if a temperature difference between photosphere and spots of 1500 K is used. A Doppler imaging analysis of photospheric lines confirms a similar spot distribution. With the help of an analogous geometric two-spot model, we are able to reproduce the modulations in the residual chromospheric emissions adopting different values of ratios between the flux of plages and quiet chromosphere (5 for Halpha and 3 for CaII). Facular regions of solar type appear to be the main responsible for the modulations of chromospheric diagnostics. Both the spot/plage model and the cross-correlation between the light curve and the chromospheric line fluxes display a lead effect of plages with respect to spots (20-40 deg in longitude). The active regions of the rapidly rotating star HD171488 are similar to the solar ones in some respect, because the spot temperature is close to that of sunspot umbrae and the plage flux-contrast is consistent with the average solar values. The main differences with respect to the Sun are larger sizes and higher latitudes.

A Young-Planet Search in Visible and Infrared Light: DN Tauri, V836 Tauri, and V827 Tauri

In searches for low-mass companions to late-type stars, correlation between radial velocity variations and line bisector slope changes indicates contamination by large starspots. Two young stars demonstrate that this test is not sufficient to rule out starspots as a cause of radial velocity variations. As part of our survey for substellar companions to T Tauri stars, we identified the ~2 Myr old planet host candidates DN Tau and V836 Tau. In both cases, visible-light radial velocity modulation appears periodic and is uncorrelated with line bisector span variations, suggesting close companions of several MJup in these systems. However, high-resolution, infrared spectroscopy shows that starspots cause the radial velocity variations. We also report unambiguous results for V827 Tau, identified as a spotted star on the basis of both visible-light and infrared spectroscopy. Our results suggest that infrared follow-up observations are critical for determining the source of radial velocity modulation in young, spotted stars.

HS 2331+3905: The cataclysmic variable that has it all

We report detailed follow-up observations of the cataclysmic variable HS 2331+3905, identified as an emissionline object in the Hamburg Quasar Survey. An orbital period of 81.08 min is unambiguously determined from the detection of eclipses in the light curves of HS 2331+3905. A second photometric period is consistently detected at P 83.38 min,∼2.8% longer than P orb , which we tentatively relate to the presence of permanent superhumps. High time resolution photometry exhibits short-timescale variability on time scales of 5−6 min which we interpret as non-radial white dwarf pulsations, as well as a coherent signal at 1.12 min, which is likely to be the white dwarf spin period. A large-amplitude quasi-sinusoidal radial velocity modulation of the Balmer and Helium lines with a period ∼3.5 h is persistently detected throughout three seasons of time-resolved spectroscopy. However, this spectroscopic period, which is in no way related to the orbital period, is not strictly coherent but drifts in period and/or phase on time scales of a few days. Modeling the far-ultraviolet to infrared spectral energy distribution of HS 2331+3905, we determine a white dwarf temperature of T eff 10 500 K (assuming M wd = 0.6 M ), close to the ZZ Ceti instability strip of single white dwarfs. The spectral model implies a distance of d = 90 ± 15 pc, and a low value for the distance is supported by the large proper motion of the system, µ = 0.14 yr −1 . The non-detection of molecular bands and the low J, H, and K fluxes of HS 2331+3905 make this object a very likely candidate for a brown-dwarf donor.

Simulations of spectral lines from an eccentric precessing accretion disc

Two-dimensional smoothed particle hydrodynamics (SPH) simulations of a precessing accretion disc in a q= 0.1 binary system (such as XTE J1118+480) reveal complex and continuously varying shape, kinematics and dissipation. The stream–disc impact region and disc spiral density waves are prominent sources of energy dissipation. The dissipated energy is modulated on the period Psh= (P−1orb−P−1prec)−1 with which the orientation of the disc relative to the mass donor repeats. This superhump modulation in dissipation energy has a variation in amplitude of ∼10 per cent relative to the total dissipation energy and evolves, repeating exactly only after a full disc precession cycle. A sharp component in the light curve is associated with centrifugally expelled material falling back and impacting the disc. Synthetic trailed spectrograms reveal two distinct ‘S-wave’ features, produced respectively by the stream gas and the disc gas at the stream–disc impact shock. These S-waves are non-sinusoidal, and evolve with disc precession phase. We identify the spiral density wave emission in the trailed spectrogram. Instantaneous Doppler maps show how the stream impact moves in velocity space during an orbit. In our maximum entropy Doppler tomogram, the stream impact region emission is distorted, and the spiral density wave emission is suppressed. A significant radial velocity modulation of the whole line profile occurs on the disc precession period. We compare our SPH simulation with a simple three-dimensional model; the former is appropriate for comparison with emission lines, while the latter is preferable for skewed absorption lines from precessing discs.

Simulating the emission line radial velocity modulation in discless intermediate polars

A code has been developed which simulates the emission line radial velocity modulation expected in a discless intermediate polar, where the bulk of the accretion flow flips from one magnetic pole to the other twice every beat cycle. The situation is found to produce a radial velocity curve which exhibits a modulation at the beat period, although this is not strictly periodic in that it is modified by an intrinsic underlying orbital modulation; i.e., the morphology of the beat modulation over one beat cycle depends on the orbital phase. Interestingly, it is found that, when the resultant velocity curve over one orbital cycle is folded on the beat period and binned coarsely, a quasisinusoidal velocity profile can be reproduced, depending on the values chosen for the various free parameters. An important implication of this result is that the spin period of BG Canis Minoris could indeed be 847 s, and is not necessarily 913 s as we had previously concluded. The model is also capable of reproducing the modulation seen in the newly discovered system RXJ1712.6–2414.

The X-ray selected cataclysmic variables H0459 + 246 and H0857 - 242

We report the discovery of two cataclysmic variables located with the assistance of X-ray positions from the HEAO 1 Modulation Collimator and the Large-Area Sky Survey. Each case is distinguished by evidence of two periodic modulations that appear to represent the orbital period and the spin period of the white dwarf, respectively. The first case, H0459 + 246, has been observed optically during faint states (V approximately 16), in which there are spectral features of both an accretion disk and a K star. The light curves in the V and I bands are consistent with ellipsoidal variations in the secondary stars with a binary period of 9.952 hr. X-ray observations with EXOSAT reveal a strong pulsation with a period approximately 62 minutes. This result confirms an 'intermediate polar' classification for H0459 + 246. The pulsation is observed at 63.2 minutes in the optical I band. The long orbital period opens the possibility that H0459 + 246 is a relatively young intermediate polar that might evolve into a polar. The second case, H0857--242, shows radial velocity modulations at 1.78 hr along with photometric variations at a period approximately 49 minutes. The latter are observed only during the decay phase of dwarf nova outbursts (13 less than V less than 17), which apparently recur frequently. Given the lack of X-ray monitoring observations and the absence of proof that the 49 minute periodicity is coherent over long time-scales, we regard H0857--242 as a candidate intermediate polar. Photographic records from th e Harvard Observatory Plate Library further reveal superoutbursts for H0857--242 (V approximately 11). A bright X-ray source that is both an intermediate polar and a continually cycling dwarf nova may provide an effective means of measuring the time delay for the arrival of accreting matter at the white dwarf surface, relative to the onset of optical brightening.

On the study of the mass ratio of spectroscopic binaries

We present a new algorithm to derive the true mass-ratio distribution of an observed sample of spectroscopic binaries. The algorithm includes an iterative procedure in which each binary of unknown inclination is replaced by an ensemble of virtual systems with a distribution of inclinations. This work shows that contrary to a widely held assumption, the inclination angles of each virtual ensemble should not be distributed randomly in space. We also suggest a way to account for the observational selection effect associated with the inability to detect single-line spectroscopic binaries with low-amplitude radial-velocity modulation

Precise radial velocities. II - A possible detection of oscillations or running waves in Aldebaran and Arcturus

view Abstract Citations (16) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Precise radial velocities. II. A possible detection of oscillations or running waves in Aldebaran and Arcturus. Smith, M. A. Abstract Reticon observations of Aldebaran and Arcturus were performed to detect any minute radial velocity modulations which could characterize the convective stellar envelopes. The observing procedure consisted of referencing small apparent shifts of the detected stellar lines near the 6300 A wavelength to telluric O2 lines in the stellar spectrum. Only radial velocity changes were sought, rather than absolute radial velocities. Measurements for the radial velocities of both stars were calculated to an accuracy within 7 m/sec. A quasiperiodicity within 16 minutes of 110 minutes was found for Aldebaran, and within 28 minutes of 97 minutes for Arcturus. The possibility of the observed global oscillations being similar to the 5-min oscillations present in the solar system sun are discussed, and further measurements are recommended. Publication: The Astrophysical Journal Pub Date: February 1983 DOI: 10.1086/160677 Bibcode: 1983ApJ...265..325S Keywords: Late Stars; Radial Velocity; Stellar Oscillations; Stellar Spectra; Correlation; Oxygen Spectra; Power Spectra; Telluric Lines; Astrophysics full text sources ADS | data products SIMBAD (3) Related Materials (1) Part 1: 1982ApJ...253..727S

The enigmatic H alpha line of FK Comae - Last stages of a coalescing binary

view Abstract Citations (69) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The enigmatic Half line of FK COM : last stages of a coalescing binary ? Walter, F. M. ; Basri, G. S. Abstract The apparently single, rapidly rotating G giant FK Comae displays an unusual hydrogen alpha emission line which is very broad, strong, and variable. Extensive high-resolution studies of this line with complete phase coverage are presented. The alpha hydrogen emission centroid shows a radial velocity modulation on the 2.4 days stellar rotation period with a semiamplitude identical to the photospheric rotational velocity. These data, when phased with optical photometry, indicate that the star has a bright, rather than dark, region on its surface and that the phase may have been stable for seven years. A qualitative model wherein the bright spot is caused by accretion from a low mass unseen companion onto the surface of the G giant is considered. Such a model explains many of the observed characteristics of the stellar spectrum and hydrogen alpha feature, and it is concluded that FK Comae is not yet a single star, but is still evolving toward coalescence of the system. Publication: The Astrophysical Journal Pub Date: September 1982 DOI: 10.1086/160293 Bibcode: 1982ApJ...260..735W Keywords: Binary Stars; Emission Spectra; G Stars; H Alpha Line; Stellar Evolution; Stellar Spectra; Stellar Spectrophotometry; High Resolution; Photosphere; Radial Velocity; Radiant Flux Density; Spectral Line Width; Spectral Resolution; Stellar Mass Accretion; Stellar Models; Stellar Rotation; Visual Photometry; Astrophysics full text sources ADS | data products SIMBAD (1)