Radial Velocity Residuals Research Articles

Stellar activity of planetary host star HD 189733

AbstractExoplanet search programs need to study how to disentangle radial-velocity (RV) variations due to Doppler motion and the noise induced by stellar activity. We monitored the active K2V HD 189733 with the high-resolution SOPHIE spectrograph (OHP, France). We refined the orbital parameters of HD 189733b and put limitations on the eccentricity and on a long-term velocity gradient. We subtracted the orbital motion of the planet and compared the variability of activity spectroscopic indices (HeI, Hα, Ca II H&K lines) to the evolution of the RV residuals and the shape of spectral lines. All are in agreement with an active stellar surface in rotation. We used such correlations to correct for the RV jitter due to stellar activity. This results in achieving a high precision on the orbital parameters, with a semi-amplitude: K=200.56±0.88m⋅s−1 and a derived planet mass of MP=1.13±0.03 MJup.

The eclipsing binary star RZ Cassiopeiae

Aims. We test the hypothesis that the oEA star RZ Cas has undergone a transient phase of rapid mass-transfer in 2000/2001. Methods. We analyze a time series of high-resolution spectra of RZ Cas obtained in 2001 and in 2006 for radial velocity (RV) and line profile variations. Improved orbital solutions are determined using the method of differential corrections. In the RV residuals, after subtracting the orbital solution and low-frequency variations, we search for non-radial pulsations in the high-frequency domain and for an amplitude modulation of the pulsation modes.We model the observed line profiles using a new computer program based on the method of spectroscopic eclipse mapping and investigate the line intensity residuals and the Rossiter-McLaughlin effect. Results. Between 2001 and 2006, the derived orbital solutions show an increase of the orbital period of the order of 2 seconds that is compatible to the photometrically obtained results. RZ Cas changed its pulsation pattern again. We find at least three pulsation frequencies where one is observed for the first time. All three frequencies show amplitude modulations that are correlated with the position of the star in its orbit. The amplitude amplification around primary minimum is much stronger than in 2001. The modeling of line profiles gives hints to a much more complex and inhomogeneous circumbinary gas density distribution in 2001 compared to 2006. The Rossiter-McLaughlin effect is strongly asymmetric in 2001 and almost normal in 2006. Conclusions. The findings support the assumption that a rapid mass-transfer episode occurred in RZ Cas in 2000/2001.

Two Jovian‐Mass Planets in Earthlike Orbits

We report the discovery of two new planets: a 1.94 M_Jup planet in a 1.8-year orbit of HD 5319, and a 2.51 M_Jup planet in a 1.1-year orbit of HD 75898. The measured eccentricities are 0.12 for HD 5319 b and 0.10 for HD 75898 b, and Markov Chain Monte Carlo simulations based on derived orbital parameters indicate that the radial velocities of both stars are consistent with circular planet orbits. With low eccentricity and 1 < a < 2 AU, our new planets have orbits similar to terrestrial planets in the solar system. The radial velocity residuals of both stars have significant trends, likely arising from substellar or low-mass stellar companions.

Formation and detectability of Earth-like planets around Alpha-Centauri B

AbstractWe simulate the late stages of planet formation around Alpha Centauri B and analyze the detectability of the resulting terrestrial planet systems. The N-body accretionary evolution of a Σ ∝ r−-1 disk populated with 400–900 lunar-mass oligarchs is followed for 200 Myr for each simulation. All of eight runs result in the formation of multiple-planet systems with at least one planet in the 1–2 M⊕ mass range at 0.5–1.5 AU. We examine the detectability of our simulated planetary systems by generating synthetic radial velocity observations including noise based on the radial velocity residuals to the recently published three planet fit to the nearby K0V star HD 69830. Using these synthetic observations, we find that we can reliably detect a 1.8 M⊕ planet in the habitable zone of α Centauri B after only three years of high cadence observations. We also find that the planet is detectable even if the radial velocity precision is 3 ms−1, as long as the noise spectrum is white.

Radial velocities of open stellar clusters: A new solid constraint favouring Tsallis maximum entropy theory

In the present study we apply a Tsallis maximum entropy distribution law to the study of the stellar residual radial velocity in a sample of 13 stellar open clusters. From a comparison between results obtained from the analysis based on Tsallis law and on the one based on the Maxwellian law we show that the generalized Tsallis distribution fits more closely the observed distribution of the stellar residual radial velocities for these stellar clusters. We have found clear evidences that the q-parameter in the Tsallis generalized distribution depends on stellar cluster ages for clusters older than 10 9 yr . There is also some indication that q increases with cluster galactocentric distance. The results obtained in this work represent an additional solid constraint in the stellar astrophysics favoring the Tsallis maximum entropy theory.

Dynamical Stability and Habitability of the γ Cephei Binary‐Planetary System

It has been suggested that the long-lived residual radial velocity variations observed in the precision radial velocity measurements of the primary of γ Cephei (HR 8974, HD 222404, HIP 116727) are likely due to a Jupiter-like planet orbiting this star. In this paper, the dynamics of this planet is studied, and the possibility of the existence of a terrestrial planet around its central star is discussed. Simulations, which have been carried out for different values of the eccentricity and semimajor axis of the binary, as well as the orbital inclination of its Jupiter-like planet, expand on previous studies of this system and indicate that, for the values of the binary eccentricity smaller than 0.5, and for all values of the orbital inclination of the Jupiter-like planet ranging from 0° to 40°, the orbit of this planet is stable. For larger values of the binary eccentricity, the system becomes gradually unstable. Integrations also indicate that, within this range of orbital parameters, a terrestrial planet, such as an Earth-like object, can have a long-term stable orbit only at distances of 0.3-0.8 AU from the primary star. The habitable zone of the primary, at a range of approximately 3.05-3.7 AU, is, however, unstable.

A massive planet to the young disc star HD 81040

We report the discovery of a massive planetary companion orbiting the young disc star HD 81040. Based on five years of precise radial-velocity measurements with the HIRES and ELODIE spectrographs, we derive a spectroscopic orbit with a period days and eccentricity . The inferred minimum mass for the companion of places it in the high-mass tail of the extrasolar planet mass distribution. From the ELODIE spectra we derive a Lithium abundance of , and from the HIRES spectra of the cores of the Ca II H and K lines we derive an activity index of , suggesting an age of about 0.8 Gyr. The radial-velocity residuals exhibit a scatter significantly larger than the typical internal measurement precision of the instruments. We attribute this excess velocity jitter to activity on the surface of the moderately young host star. However, the amplitude of the jitter is much too small and the expected period of rotation is much too short to explain the observed orbital motion, which we conclude is due to a massive planetary companion.

The HARPS search for southern extra-solar planets

We present here the discovery and characterisation of a very light planet around HD4308. The planet orbits its star in 15.56 days. The circular radial-velocity variation presents a tiny semi-amplitude of 4.1 m/s that corresponds to a planetary minimum mass m2sin(i)=14.1 Earth masses. The planet was unveiled by high-precision radial-velocity measurements obtained with the HARPS spectrograph on the ESO 3.6-m telescope. The radial-velocity residuals around the Keplerian solution are 1.3 m/s, demonstrating the very high quality of the HARPS measurements. Activity and bisector indicators exclude any significant perturbations of stellar intrinsic origin, which supports the planetary interpretation. Contrary to most planet-host stars, HD4308 has a marked sub-solar metallicity ([Fe/H]=-0.31), raising the possibility that very light planet occurrence might show a different coupling with the parent star's metallicity than do giant gaseous extra-solar planets. Together with Neptune-mass planets close to their parent stars, the new planet occupies a position in the mass-separation parameter space that is constraining for planet-formation and evolution theories. The question of whether they can be considered as residuals of evaporated gaseous giant planets, ice giants, or super-earth planets is discussed in the context of the latest core-accretion models.

The HARPS search for southern extra-solar planets

We report on the detection of three Saturn-mass planets discovered with the HARPS instrument. HD 93083 shows radial-velocity (RV) variations best explained by the presence of a companion of 0.37 M_Jup orbiting in 143.6 days. HD 101930 b has an orbital period of 70.5 days and a minimum mass of 0.30 M_Jup. For HD 102117, we present the independent detection of a companion with m2sini = 0.14 M_Jup and orbital period P = 20.7 days. This planet was recently detected by Tinney et al. (2004). Activity and bisector indicators exclude any significant RV perturbations of stellar origin, reinforcing the planetary interpretation of the RV variations. The radial-velocity residuals around the Keplerian fits are 2.0, 1.8 and 0.9 m/s respectively, showing the unprecedented RV accuracy achieved with HARPS. A sample of stable stars observed with HARPS is also presented to illustrate the long-term precision of the instrument. All three stars are metal-rich, confirming the now well-established relation between planet occurrence and metallicity. The new planets are all in the Saturn-mass range, orbiting at moderate distance from their parent star, thereby occupying an area of the parameter space which seems difficult to populate according to planet formation theories. A systematic exploration of these regions will provide new constraints on formation scenarios in the near future.

Disentangling component spectra of , a spectroscopic binary with a pulsating primary

A new reduction and a new analysis of a rich series of high-S/N spectra of the bright star κ Sco is carried out to test the technique of spectral disentangling in the case when one of the components is a non-radial oscillator. We im- prove the orbital elements of the system and find the basic physical properties of the binary to be Teff = 24 500 K, masses of 10.7-11.9 Mand 9.6-10.7 Mand the primary radius and rotational period of 7-8 Rand 3 d .56-3 d68, respectively. This also implies log g = 3.70-3.78 (cgs). KOREL disentangling is applied and we find that it worked properly and was not misled by the complex line-profile variability of the pulsating primary. Moreover, the pulsational frequencies are detected via the period search in the line intensities and radial-velocity residuals of the primary derived by KOREL and in the time series of residual spectra in the rest frame of the primary after KOREL disentangling. This constitutes a much better starting point to interpret the complex pixel-by-pixel variations of the disentangled profiles of the primary in terms of stellar oscillations and/or additional rotational modulation than the original spectra before disentangling.

A Planetary Companion to γ Cephei A

We report on the detection of a planetary companion in orbit around the primary star of the binary system γ Cephei. High-precision radial velocity measurements using four independent data sets spanning the time interval 1981-2002 reveal long-lived residual radial velocity variations superposed on the binary orbit that are coherent in phase and amplitude with a period or 2.48 yr (906 days) and a semiamplitude of 27.5 m s-1. We performed a careful analysis of our Ca II H and K S-index measurements, spectral line bisectors, and Hipparcos photometry. We found no significant variations in these quantities with the 906 day period. We also reanalyzed the Ca II λ8662 measurements of Walker et al., which showed possible periodic variations with the "planet" period when first published. This analysis shows that periodic Ca II equivalent width variations were only present during 1986.5-1992 and absent during 1981-1986.5. Furthermore, a refined period for the Ca II λ8662 variations is 2.14 yr, significantly less than the residual radial velocity period. The most likely explanation of the residual radial velocity variations is a planetary-mass companion with M sin i = 1.7MJ and an orbital semimajor axis of a2 = 2.13 AU. This supports the planet hypothesis for the residual radial velocity variations for γ Cep first suggested by Walker et al. With an estimated binary orbital period of 57 yr, γ Cep is the shortest period binary system in which an extrasolar planet has been found. This system may provide insights into the relationship between planetary and binary star formation.

Periodic pattern in the residual velocity field of OB-Associations

Abstract An analysis of the space velocity field of the OB-associations within 3 kpc of the Sun revealed a periodic pattern in the residual radial velocity field along the galactic radius-vector with a typical scale length of λ = 2.0 ± 0.2 and a mean amplitude of f R = 7 ± 1 km s−1. The fact that the radial residual velocities of almost all OB-associations in rich star-gas complexes are directed toward the Galactic center proves that the region considered is inside the corotation circle. The azimuthal velocity field of OB-associations exhibits a well-defined periodicity in the region l 180°. The galactocentric distances of the Cygnus and Perseus arms as inferred from separate analyses of radial and azimuthal residual velocity fields agree with each other within the errors.

The Radial Velocity and Spectral Line Bisector Variability of Polaris

We present precise stellar radial velocity measurements for the Cepheid-type star Polaris taken in 1992–1993. The peak-to-peak amplitude of the pulsations was 1.555 ± 0.056 km s-1 in epoch 1992.4 and 1.517 ± 0.047 km s-1 in epoch 1993.2. These amplitudes are comparable to the one measured by Dinshaw et al. in 1987.75 and recent measurements by Kamper &Fernie for 1995–1997. Consequently, these do not support the continued drop in pulsational amplitude first extrapolated by Dinshaw et al. A periodogram analysis for our data yields a pulsational period of 39726769 ± 000011, slightly higher than the value found by Dinshaw et al. and consistent with the value derived from the Kamper &Fernie data. The pulsational period of Polaris may thus be increasing. Residual radial velocity measurements after removal of the component due to radial pulsations show the presence of a 40 day period with a 2K amplitude of about 400 m s-1, first reported by Dinshaw et al. Spectral line bisectors of the Sc II λ5526 and Mg I λ5528 lines also show variations with the 40 day period, strongly indicating that this period is indeed real. The presence of line bisector variations excludes a low-mass companion object as a cause of the residual radial velocity variations. Two models are considered for the residual radial velocity and bisector span variations: starspots and nonradial pulsations. Although both can reproduce the amplitude and shape of the residual radial velocity variations, the spot models considered were unable to reproduce the overall shape and amplitude of the bisector span variations. The best-fit spot model was provided by a single spot with a temperature 500 K cooler than the photosphere with a macroturbulent velocity of zero in the spot. If surface features do exist on Polaris and are responsible for the residual radial variations for this star, then possibly they have a temperature structure and distribution more complicated than the simple models considered here. The best fit to all the observed variations was provided by a nonradial m = 4 mode, although these were not entirely satisfactory having a phase shift of about 0.25 between the observed and predicted bisector variations. Possible explanations for this shift include temperature effects, a source function originating in a dynamic stellar atmosphere, or a different pulsation mode than the one that was considered. Although the exact pulsational mode is yet to be identified, we believe that the residual radial velocity variations are due to a long-period pulsation mode. Supporting evidence comes from the fact that three different residual variations with periods near 40 days have now been seen in Polaris and it is unlikely that these variations are due to rotational modulation by surface features on a star that is differentially rotating.

Long-period, low-amplitude radial velocity variations in the K giant star Herculis: rotation, substellar companion or non-radial pulsations?

Precise stellar radial velocity (RV) measurements (σ≈ 20 m s-1 ) spanning more than 2 yr are presented for the K giant star π Herculis. These show variability with a period of 613 ± 57 d and an amplitude of 150 ± 12 m s-1 . Radial pulsations can be excluded as a mechanism for this variability because the observed period is more than an order of magnitude greater than the expected period of the fundamental radial mode. Tenable hypotheses for the RV variability include rotational modulation by surface structure, non-radial pulsations, or a substellar companion of mass at least 27 MJupiter in orbit 3 au from the star. An upper limit of 1400 d to the rotational period for π Herculis is determined using published values of the angular diameter and distance to π Herculis as well as an estimate of the projected rotational velocity. Rotational modulation is thus a viable mechanism for the RV variability. The RV variations were also fitted using two models: (i) a stellar surface covered with cool spots and (ii) non-radial pulsations. Both models could adequately reproduce the RV curve although the spot model predicts photometric variations of Δ V ∼ 0.1 mag. As a result of the long period, non-radial pulsations may be g-mode or r-mode oscillations, which implies that most of the atmospheric motion of the star is in the horizontal direction. If these modes are indeed present then the corresponding photometric amplitude for non-radial pulsations may be quite small. The radial velocity variations were also measured using subsections of the spectral region. Weak spectral lines yielded an RV amplitude of ≈ 140 m s-1 whereas the stronger lines yielded an RV amplitude of ≈ 220 m s-1 with a phase shift of about 60 ° with respect to the weaker lines. This seems to support the pulsation hypothesis as the cause of the RV variability, although an analysis of more lines is needed to confirm this. Also, a period of 90.3 d with an amplitude 50 m s-1 is found in the residual RV measurements after subtracting the 613-d component. The presence of two periods also argues in favour of non-radial pulsations, although at the present time one cannot exclude low-mass companions or surface structure as a cause for at least one of the observed periods. Photometric measurements as well as detailed analysis of the changes in the spectral line shapes using high-resolution data may be required to distinguish between the companion object and non-radial pulsation hypotheses.

An analysis of the radial velocity residuals for various models of SS 433

view Abstract Citations (4) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Analysis of the Radial Velocity Residuals for Various Models of SS 433 Collins, George W., II ; Garasi, Christopher J. Abstract In this paper we analyze the residuals resulting from the comparison of several models with radial velocity data for the jets of SS 433. We find no compelling evidence for random variations in orientation or speed of the relativistic jets commonly known as 'jitter.' Earlier determinations of the presence of 'jitter' can be traced to the incomplete modeling of the nodding motion of the jets. Such motion results from the time-dependent torques originating with the motion of the companion. While it is likely that such "jitter" exists, its presence is below the detectable limit of contemporary analysis. We conclude that at the present time even the best models for the motions of SS 433 appear to be incomplete on timescales exceeding a few years. Detection of the jitter will require an improvement in both the volume of data available for analysis as well as improvements in the models for the motion of the jets. Publication: The Astrophysical Journal Pub Date: August 1994 DOI: 10.1086/174534 Bibcode: 1994ApJ...431..836C Keywords: Doppler Effect; Radial Velocity; Radio Jets (Astronomy); Stochastic Processes; Astronomical Spectroscopy; Cosmology; Distribution Functions; Kinematics; Time Dependence; Astrophysics; STARS: BINARIES: SPECTROSCOPIC; STARS: INDIVIDUAL ALPHANUMERIC: SS 433; TECHNIQUES: RADIAL VELOCITIES full text sources ADS | data products SIMBAD (1)

Multiple stars: Anathemas or friends?

Multiple systems are generally divided into two groups: Trapezium systems and hierarchical systems. Trapezium systems consist of three or more stars whose separations are roughly equal. These systems are expected to be dynamically unstable. In hierarchical systems successive separations increase by large factors. The multiplicity of such hierarchies may be detected by a number of different techniques including astrometry, spectroscopy, photometry and speckle interferometry. Photometrically, an eclipsing system orbiting a third star will have periodic changes in eclipse timings as a result of light travel time effects. This manifests itself as an apparent change of the eclipse period. Another detectable effect is the precession of the line of nodes, resulting in a change of the inclination of the eclipsing pair. Such nodal precession may also be detected spectroscopically as a change in the semiamplitude of the orbit. Also, unexpectedly large and/or systematic radial velocity residuals often indicate a change in the center-of-mass velocity of the short period system due to orbital motion about a third component. Observational examples of such occurences are discussed. Finally, preliminary theoretical work on multiple star stability and formation is discussed and compared in some cases with observations.

The stellar disk component: distribution, motions, age and stellar composition

The distribution of the stellar disk component is studied with particular emphasis on the properties of open clusters. A scale height of 80 pc is found for clusters younger than 109years while the scale height is 200 pc for older clusters. A radial metallicity gradient in the disk is confirmed but there seem to be significant abundance variations apart from this. There are radial gradients in age as well as in linear diameter. Kinematically, there are a number of regions in the Milky Way with systematic radial velocity residuals.

The Kinematics of the Local Supercluster

The spatial distribution of galaxies in the Local Supercluster, as described at this meeting, together with the measured anisotropy in the microwave background suggest that there exist significant deviations from a uniform Hubble flow in the velocity field of galaxies within a few thousand km/s. In principle, it is not too hard to improve on the uniform flow model: one simply needs to examine the spatial distribution of the radial velocity residuals for many nearby galaxies. In practice, the problem is non-trivial because of the coupling of velocity and distance, and the lack of a distance indicator of high precision, and the “thermal” noise in the velocity field. Our recent efforts in this direction are described in more detail in a paper in a current Astrophysical Journal (Aaronson et al. 1982a).

A Comparison of the Components in Interstellar Sodium and Calcium.

view Abstract Citations (254) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Comparison of the Components in Interstellar Sodium and Calcium. Routly, Paul McRae ; Spitzer, Lyman, Jr. Abstract Radial velocities and equivalent widths of the interstellar D lines, including a number of faint components, were obtained for some twenty stars from high-dispersion spectrograms taken at the Mount Wilson Observatory. Corresponding measures in Ca II were also obtained for four stars. This material, together with additional measures obtained previously by other investigators, was employed in a comparison between Na and Ca. For each component N(Na I) and N(Ca II), the numbers of absorbing Na I atoms and Ca II ions in the line of sight, were found whenever possible, as were also the values of the Doppler widths b(Na I) and b(Ca II). For strong components, the data indicate that b(Ca II) in kilometers per second is about 1.5 times b(Na I), in qualitative agreement with Wilson's analysis; but for weaker lines these Doppler widths are more nearly equal. On the average, a decrease occurs in N(Na I)/N(Ca II) as the residual radial velocity of the component increases in absolute value; in low-velocity clouds Na I tends to be more abundant than Ca II, while in high-velocity clouds the reverse is true. This result apparently explains why the strong saturated lines of Na I and Ca II do not lie on the same curve of growth [b(Ca II) > b(Na I)]. Consideration is given to the possibility that differences of ionization between high-velocity and low-velocity clouds may this variation of abundance ratio with cloud velocity. In a rapidly moving cloud the kinetic temperature should be increased, since the intercloud gas in front of the cloud will be compressed and heated. At a temperature somewhere between 5000°and 10,000°, collisional ionization of Na I by electrons would reduce the ratio N(Na I)/N(Ca II) by the observed factor. However it is uncertain whether the temperature can be so high, and other mechanisms may be important. Publication: The Astrophysical Journal Pub Date: March 1952 DOI: 10.1086/145535 Bibcode: 1952ApJ...115..227R full text sources ADS | data products SIMBAD (25)

A comparison of the interstellar lines and components in neutral sodium and singly ionized calcium.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A comparison of the interstellar lines and components in neutral sodium and singly ionized calcium. Routly, Paul Mcrae ; Spitzer, Lyman, Jr. Abstract New measures of the radial velocities and equivalent widths of the interstellar D lines of Nai, including faint components, were obtained for 17 stars from high dispersion spectrograms taken at the Mount Wilson Observatory. Corresponding measures in Caii were also obtained for four stars. The new material on Nai, together with additional measures obtained previously by other investigators, was employed in a comparison with Caii. For each line, or component, for which reliable equivalent widths were available in both Nai and Caii, the total number of absorbing atoms (or ions) in the line of sight was computed, N~a1 and Ncass, as were also the values of the Doppler constants b(Nai) and b(Caii). For saturated lines, the data verify the result of Wilson's that b(Caii) 2 or 3 X b(Nai). A plot of Nxai/Ncaii versus the residual radial velocity V of the corresponding cloud producing the line or component shows that on the average a marked decrease occurs in Nxes/Nce,1 as V increases; in low velocity clouds Nai tends to be more abundant than Caii, while in high velocity clouds the reverse is true. This result may be used to give a plausible explanation for the fact that the saturated lines of Nai and Caii do not lie on the same curve of growth, b(Caii) > b(Nai). The theoretical question of the kinetic temperature prevailing in a high velocity cloud, as a result of the cloud's motion through an inter- cloud medium, was considered from two points of view. The two methods stand at opposite physical extremes and, except in one case regarded as unrealistic, give discordant values of the temperature. The computations indicate that the kinetic temperature in a cloud possessing a residual radial velocity of 8o km/sec should lie somewhere between 20000 and 13,0000, with the lower value considered more likely. The level of ionization in low and high velocity clouds was considered next in an effort to explain the observed variation of Nxas/Nca1s as a function of V. It is shown that for a high velocity cloud having an internal kinetic temperature in the vicinity of 70000 to 10,0000, collisional ionization of Nai by electrons will be sufficiently effective to reduce the value of Nxas/Ncasi by a factor of from 50 to 100 times that which it would possess in a low velocity cloud (~Io00). This theoretical variation is ample to account for the observational data, provided the kinetic temperatures in a high velocity cloud are actually as high as 70000. When the kinetic temperature inside a cloud is less than 70000, the ionization of Nai by electron collisions is insensible; to allow for such cases, several other mechanisms which would affect the ratio N~a5/N~a1i were suggested, but were not analyzed quantitatively. Princeton University Observatory, Princeton, N. J. Publication: The Astronomical Journal Pub Date: 1951 DOI: 10.1086/106620 Bibcode: 1951AJ.....56R.138R full text sources ADS |