- ID:
- ivo://CDS.VizieR/J/other/Nat/563.365
- Title:
- Barnard's star radial velocity curve
- Short Name:
- J/other/Nat/563.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Barnard's star is a red dwarf, and has the largest proper motion (apparent motion across the sky) of all known stars. At a distance of 1.8 parsecs, it is the closest single star to the Sun; only the three stars in the α Centauri system are closer. Barnard's star is also among the least magnetically active red dwarfs known and has an estimated age older than the Solar System. Its properties make it a prime target for planetary searches; various techniques with different sensitivity limits have been used previously, including radial-velocity imaging, astrometry and direct imaging, but all ultimately led to negative or null results. Here we combine numerous measurements from high-precision radial-velocity instruments, revealing the presence of a low-amplitude periodic signal with a period of 233 days. Independent photometric and spectroscopic monitoring, as well as an analysis of instrumental systematic effects, suggest that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard's star is a cold super-Earth, with a minimum mass of 3.2 times that of Earth, orbiting near its snow line (the minimum distance from the star at which volatile compounds could condense). The combination of all radial-velocity datasets spanning 20 years of measurements additionally reveals a long-term modulation that could arise from a stellar magnetic-activity cycle or from a more distant planetary object. Because of its proximity to the Sun, the candidate planet has a maximum angular separation of 220 milliarcseconds from Barnard's star, making it an excellent target for direct imaging and astrometric observations in the future.
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- ID:
- ivo://CDS.VizieR/J/AJ/159/50
- Title:
- Identifying multiple populations in M71 using CN
- Short Name:
- J/AJ/159/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed their cyanogen CN features at ∼3800 and 4120Å as well as the CH band at ∼4300Å for 145 evolved stars in the Galactic globular cluster M71 using the multi-object spectrograph, Hydra, on the Wisconsin-Indiana-Yale- NOAO-3.5 m telescope. We use these measurements to create two δCN indices finding that both distributions are best fit by two populations: a CN-enhanced and CN-normal. We find that 42%±4% of the red giant branch stars in our sample are CN-enhanced. The percentage of CN-enhanced is 40%±13% for the asymptotic giant branch and 33%±9% for the horizontal branch stars (HB stars), which suggests there are no missing second generation stars at these stages of stellar evolution. The two generations also separate in magnitude and color on the HB, which allows us to find the difference in He abundance between the two populations by fitting appropriate zero-age horizontal branches. The broad range of distances from the cluster's center covered by our sample allows us to study the dependence of the ratio of the number of first to second population stars on the distance from the cluster's center, and we find that this ratio does not vary radially and that the two populations are spatially mixed. Finally, we compare our identification of multiple populations with the classification based on the Na-O anti-correlation and the Hubble Space Telescope UV photometry, and we find good agreement with both methods.
- ID:
- ivo://CDS.VizieR/J/other/Nat/481.475
- Title:
- Radial velocities of Kepler-34b & Kepler-35b
- Short Name:
- J/other/Nat/481.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most Sun-like stars in the Galaxy reside in gravitationally bound pairs of stars (binaries). Although long anticipated the existence of a 'circumbinary planet' orbiting such a pair of normal stars was not definitively established until the discovery of the planet transiting (that is, passing in front of) Kepler-16. Questions remained, however, about the prevalence of circumbinary planets and their range of orbital and physical properties. Here we report two additional transiting circumbinary planets: Kepler-34(AB)b and Kepler-35(AB)b, referred to here as Kepler-34b and Kepler-35b, respectively. Each is a low-density gas-giant planet on an orbit closely aligned with that of its parent stars. Kepler-34b orbits two Sun-like stars every 289 days, whereas Kepler-35b orbits a pair of smaller stars (89% and 81% of the Sun's mass) every 131 days. The planets experience large multi-periodic variations in incident stellar radiation arising from the orbital motion of the stars. The observed rate of circumbinary planets in our sample implies that more than ∼1% of close binary stars have giant planets in nearly coplanar orbits, yielding a Galactic population of at least several million.
- ID:
- ivo://CDS.VizieR/J/AJ/110/2288
- Title:
- RR Lyrae Metallicities
- Short Name:
- III/176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog presents metal abundance, distance and radial velocity data on a sample of 302 ab-type RR Lyrae variables within about 2.5 kpc of the Sun. The metal abundance information was obtained from low-medium resolution spectra, using the pseudo-equivalent widths of the Ca II K line and the the H-delta, H-gamma and H-beta lines. The technique employed was similar to Preston's (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1959ApJ...130..507P%201959ApJ...130..507P">1959ApJ...130..507P 1959ApJ...130..507P</A>) Δ-S method, though significant differences exist; see the source reference for details. The data were calibrated to the Zinn & West (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1984ApJS...55...45Z%201984ApJS...55...45Z">1984ApJS...55...45Z 1984ApJS...55...45Z</A>) globular cluster abundance scale. The photometry employed in the distance determinations was primarily taken from the General Catalog of Variable Stars (1985, hereafter GCVS4). Exceptions are noted in column 29; the letters match the footnotes in Table 10 of Layden (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1994AJ....108.1016L%201994AJ....108.1016L">1994AJ....108.1016L 1994AJ....108.1016L</A>). The minimum and maximum light photometry, and rise-time were combined following Barnes & Hawley (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1986ApJ...307L...9B%201986ApJ...307L...9B">1986ApJ...307L...9B 1986ApJ...307L...9B</A>) to give an estimate of the intensity- averaged magnitude, i.e. the magnitude the star would have if it were not variable. When the GCVS4 quoted magnitudes in passbands other than V, the GCVS4 magnitudes were transformed to the V passband using the relations established in Layden (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1994AJ....108.1016L%201994AJ....108.1016L">1994AJ....108.1016L 1994AJ....108.1016L</A>). The interstellar absorption estimates are from Burstein & Heiles (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1982AJ.....87.1165B%201982AJ.....87.1165B">1982AJ.....87.1165B 1982AJ.....87.1165B</A>), modified by a simple dust-distribution model. The distances were computed assuming the Mv(RR)-[Fe/H] relation of Carney, Storm & Jones (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1992ApJ...386..663C%201992ApJ...386..663C">1992ApJ...386..663C 1992ApJ...386..663C</A>). Radial velocities were measured from the spectra via cross-correlation with secondary velocity standards. The velocities from the individual spectra were fit with a standard radial velocity curve in the (phase, velocity) plane, to give an estimate of the systemic (center of mass) velocity of each star. The error in this value was estimated from the scatter about the best-fit velocity curve, and the quality of the spectra employed. Other methods were used to combine the individual velocities when the situation demanded (cm = 2,3 in column 70; see Layden (<A HREF="http://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=1994AJ....108.1016L%201994AJ....108.1016L">1994AJ....108.1016L 1994AJ....108.1016L</A>) for details). The observed velocities were combined with values from the literature to produce a final, best estimate of the systemic radial velocity of each star, and its error.
