Stellar jitter from variable gravitational redshift: implications for RV confirmation of habitable exoplanets

A variation of gravitational redshift, arising from stellar radius fluctuations, will introduce astrophysical noise into radial velocity measurements by shifting the centroid of the observed spectral lines. Shifting the centroid does not necessarily introduce line asymmetries. This is fundamentally different from other types of stellar jitter so far identified, which do result from line asymmetries. Furthermore, only a very small change in stellar radius, ~0.01%, is necessary to generate a gravitational redshift variation large enough to mask or mimic an Earth-twin. We explore possible mechanisms for stellar radius fluctuations in low-mass stars. Convective inhibition due to varying magnetic field strengths and the Wilson depression of starspots are both found to induce substantial gravitational redshift variations. Finally, we investigate a possible method for monitoring/correcting this newly identified potential source of jitter and comment on its impact for future exoplanet searches.Comment: 6 pages, 1 figure, 1 tabl

Solar apparent radius variability: a new statistical approach to astrolabe multi-site observations

Monthly Notices of the Royal Astronomical Society, v. 369, n. 1, p. 8388, 2006. http://dx.doi.org/10.1111/j.1365-2966.2006.10248.xInternational audienceIn summer 1999, we performed a survey optimized for the discovery of irregular satellites of Uranus and Neptune. We imaged 11.85 deg 2 of sky and discovered 66 new outer Solar system objects (not counting the three new Uranian satellites). Given the very short orbital arcs of our observations, only the heliocentric distance can be reliably determined. We were able to model the radial distribution of trans-Neptunian objects (TNOs). Our data support the idea of a strong depletion in the surface density beyond 45 au. After fully characterizing this survey's detection efficiency as a function of object magnitude and rate of motion, we find that the apparent luminosity function of the trans-Neptunian region in the range m R = 22-25 is steep with a best-fitting cumulative power-law index of α 0.76 with one object per deg 2 estimated at magnitude R o = 23.3. This steep slope, corresponding to a differential size index of q 4.8, agrees with other older and more recent analyses for the luminosity function brighter than 25 mag. A double power-law fit to the new data set turns out to be statistically unwarrented; this large and homogeneous data set provides no evidence for a break in the power-law slope, which must eventually occur if the Bernstein et al. sky density measurements are correct

Influence of the UTLS region on the astrolabes solar signal measurement

International audienceRegular measurements of the Sun's diameter have been obtained by means of solar astrolabes for several decades. However, the variations found from those measurements are still very controversial, and the results implying changes in the solar radius are not conclusive. Since the quality of the measurements cannot be doubted, it is necessary to wonder what they are actually observing. We show here that some refraction effects, neglected so far, must be taken into account. Then, if the lower atmospheric layers merely add high-frequency noise (validated by the measured Fried parameter), we show here that the mid- to long-term variations take root in the upper troposphere - lower stratosphere region. Hence, the annual means of the Sun's apparent radius, measured at Calern (France) and Santiago (Chile), are linearly correlated with the geopotential height at 50-100 mb with correlation coefficients of -0.66 and 0.62, respectively, the opposite signs being the signature of the symmetry of the two hemispheres, North and South. In addition, the measurement dispersion is correlated with the variance of the wind speed above each observatory. Thus, it appears that the solar signal is amplified by the mechanisms dwelling in this interface zone between the lower stratosphere and the upper troposphere. Because these amplification mechanisms are unknown, it is difficult to extract pure solar information from the astrolabe signals, especially in sites where the seeing is less than 14-16 cm

History of solar oblateness measurements and interpretation

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