The low-level radial velocity variability in Barnard's star (= GJ 699) ? Secular acceleration, indications for convective redshift, and planet mass limits

By M. Kuerster, M. Endl, F. Rouesnel, S. Els, A. Kaufer, S. Brillant, A. Hatzes, S. Saar, W. P. T. L. Tautenburg, M. Observatory and 4 more. 2003

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We report results from 2 1=2 yr of high precision radial velocity (RV) monitoring of Barnard's star. The high RV measurement precision of the VLT-UT2+UVES of 2:65 m s 1 made the following findings possible. (1) The first detection of the change in the RV of a star caused by its space motion (RV secular acceleration). (2) An anti-correlation of the measured RV with the strength of the filling-in of the H line by emission. (3) Very stringent mass upper limits to planetary companions. Using only data from the first 2 years, we obtain a best-fit value for the RV secular acceleration of 5:15 0:89 m s 1 yr 1 .T his agrees within 0:95 with the predicted value of 4:50 m s 1 yr 1 based on the Hipparcos proper motion and parallax combined with the known absolute radial velocity of the star. When the RV data of the last half-year are added the best-fit slope is strongly reduced to 2:97 0:51 m s 1 yr 1 (3:0 away from the predicted value), clearly suggesting the presence of additional RV variability in the star. Part of it can be attributed to stellar activity as we demonstrate by correlating the residual RVs with an index that describes the filling-in of the H line by emission. A correlation coecient of 0:50 indicates that the appearance of active regions causes a blueshift of photospheric absorption lines. Assuming that active regions basically inhibit convection we discuss the possibility that the fundamental (inactive) convection pattern in this M4V star produces a convective redshift which would indicate that the majority of the absorption lines relevant for our RV measurements is formed in a region of convective overshoot. This interpretation could possibly extend a trend indicated in the behaviour of earlier spectral types that exhibit convective blueshift, but with decreasing line asymmetries and blueshifts as one goes from G to K dwarfs. Based on this assumption, we estimate that the variation of the visible plage coverage is about 20%. We also determine upper limits to the projected mass m sin i and to the true mass m of hypothetical planetary companions in circular orbits. For the separation range 0:017 0:98 AU we exclude any planet with m sin i> 0:12 MJupiter and m> 0:86 MJupiter. Throughout the habitable zone around Barnard's star, i.e. 0:034 0:082 AU, we exclude planets with m sin i> 7:5 MEarth and m> 3:1 MNeptune.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/30f553e0608da236c099b44eb68c341a97f8a9a1

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Citations in the corpus

Catalog of Nearby Exoplanets (2006, background): “Other Doppler programs have contributed important discoveries of nearby planets (Cochran et al. 1997; Endl et al. 2003; Noyes et al. 1999; Kürster et al. 2003; Charbonneau et al. 2000; Sato et al. 2005).”
The planet search programme at the ESO CES and HARPS - IV. The search for Jupiter analogues around solar-like stars (2012, background): “This perspective effect can become a measurable positive trend in some high proper motion stars (Schlesinger 1917; Kürster et al. 2003; Zechmeister et al. 2009).”
Detection Limits from the McDonald Observatory Planet Search Program (2006, methodology): “…colleagues on southern hemisphere radial velocity surveys using the facilities of ESO at La Silla and the VLT (Kürster et al. 2000; Endl et al. 2002; Kürster et al. 2003), and a program to use the Keck 1 HIRES spectrograph to search for planetary companions to stars in the Hyades (Cochran et al.…”
THE NIRSPEC ULTRACOOL DWARF RADIAL VELOCITY SURVEY (2010, methodology): “We calculated the secular RV acceleration (dRV/dt) for this object following Kürster et al. (2003) and estimated the maximum amplitude of this effect to be less than 0.6 m s−1 yr−1, far smaller than the observed trend.”
Stellar and substellar companions of nearby stars from Gaia DR2 (2018, methodology): “For Proxima, Barnard’s star (GJ 699) and Kapteyn’s star (GJ 191), we took into account secular accelerations of +0.45 m s−1 a−1 (Endl & Kürster 2008), +4.50 m s−1 a−1 (Kürster et al. 2003) and −0.18 m s−1 a−1 (Anglada-Escudé et al. 2014), respectively.”
THE CALIFORNIA PLANET SURVEY. I. FOUR NEW GIANT EXOPLANETS (2010, background): “As discussed in Kürster et al. (2003) and Wright & Howard (2009), a star’s proper motion will cause the the radial component of its space velocity vector to change with position on the sky, resulting a secular acceleration of v̇r = Dµ 2 (to first order), where vr is the bulk radial velocity of the…”
The HARPS search for southern extra-solar planets. X. A m sin i = 11 M_â planet around the nearby spotted M dwarf GJ 674 (2007, background): “Similar to Kürster et al. (2003), we define our Hα index as Index = FHα F1 + F2 , (2) with FHα sampling the Hα line, and F1 and F2 the continuum on both sides of the line.”