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Title: No Conclusive Evidence for Transits of Proxima b in MOST Photometry

Abstract

The analysis of Proxima Centauri’s radial velocities recently led Anglada-Escudé et al. to claim the presence of a low-mass planet orbiting the Sun’s nearest star once every 11.2 days. Although the a priori probability that Proxima b transits its parent star is just 1.5%, the potential impact of such a discovery would be considerable. Independent of recent radial velocity efforts, we observed Proxima Centauri for 12.5 days in 2014 and 31 days in 2015 with the Microwave and Oscillations of Stars space telescope. We report here that we cannot make a compelling case that Proxima b transits in our precise photometric time series. Imposing an informative prior on the period and phase, we do detect a candidate signal with the expected depth. However, perturbing the phase prior across 100 evenly spaced intervals reveals one strong false positive and one weaker instance. We estimate a false-positive rate of at least a few percent and a much higher false-negative rate of 20%–40%, likely caused by the very high flare rate of Proxima Centauri. Comparing our candidate signal to HATSouth ground-based photometry reveals that the signal is somewhat, but not conclusively, disfavored (1 σ –2 σ ), leading us to argue that themore » signal is most likely spurious. We expect that infrared photometric follow-up could more conclusively test the existence of this candidate signal, owing to the suppression of flare activity and the impressive infrared brightness of the parent star.« less

Authors:
; ;  [1];  [2]; ; ; ;  [3];  [4];  [5];  [6];  [7];  [8];  [9];  [10]; ;  [11];
  1. Department of Astronomy, Columbia University, 550 W. 120th Street, New York, NY 10027 (United States)
  2. Department of Mathematics, Physics and Geology, Cape Breton University, 1250 Grand Lake Road, Sydney, NS B1P 6L2 (Canada)
  3. Department of Astrophysical Sciences, 4 Ivy Lane, Princeton, NJ 08544 (United States)
  4. Department of Physics and Astronomy, Western Washington University, 516 High Street, Bellingham, WA 98225 (United States)
  5. Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada)
  6. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  7. Observatoire Astronomque du Mont Mégantic, Départment de Physique, Université de Montréal C. P. 6128, Succursale, Centre-Ville, Montréal, QC H3C 3J7 (Canada)
  8. Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117 (United States)
  9. Instituto de Astrofísica, Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago (Chile)
  10. Observatoire Astronomique de Universite de Genéve, 51 ch. des Maillettes, 1290 Versoix (Switzerland)
  11. Max Plank Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
Publication Date:
OSTI Identifier:
22663966
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 3; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BRIGHTNESS; COMPARATIVE EVALUATIONS; MAIN SEQUENCE STARS; MASS; MICROWAVE RADIATION; OSCILLATIONS; PHOTOMETRY; PLANETS; RADIAL VELOCITY; SIGNALS; SPACE; TELESCOPES

Citation Formats

Kipping, David M., Chen, Jingjing, Sandford, Emily, Cameron, Chris, Hartman, Joel D., Bakos, Gáspár Á., Penev, Kaloyan, Csubry, Zoltan, Davenport, James R. A., Matthews, Jaymie M., Sasselov, Dimitar, Rowe, Jason, Siverd, Robert J., Jordán, Andrés, Bayliss, Daniel, Henning, Thomas, Mancini, Luigi, and and others. No Conclusive Evidence for Transits of Proxima b in MOST Photometry. United States: N. p., 2017. Web. doi:10.3847/1538-3881/153/3/93.
Kipping, David M., Chen, Jingjing, Sandford, Emily, Cameron, Chris, Hartman, Joel D., Bakos, Gáspár Á., Penev, Kaloyan, Csubry, Zoltan, Davenport, James R. A., Matthews, Jaymie M., Sasselov, Dimitar, Rowe, Jason, Siverd, Robert J., Jordán, Andrés, Bayliss, Daniel, Henning, Thomas, Mancini, Luigi, & and others. No Conclusive Evidence for Transits of Proxima b in MOST Photometry. United States. doi:10.3847/1538-3881/153/3/93.
Kipping, David M., Chen, Jingjing, Sandford, Emily, Cameron, Chris, Hartman, Joel D., Bakos, Gáspár Á., Penev, Kaloyan, Csubry, Zoltan, Davenport, James R. A., Matthews, Jaymie M., Sasselov, Dimitar, Rowe, Jason, Siverd, Robert J., Jordán, Andrés, Bayliss, Daniel, Henning, Thomas, Mancini, Luigi, and and others. Wed . "No Conclusive Evidence for Transits of Proxima b in MOST Photometry". United States. doi:10.3847/1538-3881/153/3/93.
@article{osti_22663966,
title = {No Conclusive Evidence for Transits of Proxima b in MOST Photometry},
author = {Kipping, David M. and Chen, Jingjing and Sandford, Emily and Cameron, Chris and Hartman, Joel D. and Bakos, Gáspár Á. and Penev, Kaloyan and Csubry, Zoltan and Davenport, James R. A. and Matthews, Jaymie M. and Sasselov, Dimitar and Rowe, Jason and Siverd, Robert J. and Jordán, Andrés and Bayliss, Daniel and Henning, Thomas and Mancini, Luigi and and others},
abstractNote = {The analysis of Proxima Centauri’s radial velocities recently led Anglada-Escudé et al. to claim the presence of a low-mass planet orbiting the Sun’s nearest star once every 11.2 days. Although the a priori probability that Proxima b transits its parent star is just 1.5%, the potential impact of such a discovery would be considerable. Independent of recent radial velocity efforts, we observed Proxima Centauri for 12.5 days in 2014 and 31 days in 2015 with the Microwave and Oscillations of Stars space telescope. We report here that we cannot make a compelling case that Proxima b transits in our precise photometric time series. Imposing an informative prior on the period and phase, we do detect a candidate signal with the expected depth. However, perturbing the phase prior across 100 evenly spaced intervals reveals one strong false positive and one weaker instance. We estimate a false-positive rate of at least a few percent and a much higher false-negative rate of 20%–40%, likely caused by the very high flare rate of Proxima Centauri. Comparing our candidate signal to HATSouth ground-based photometry reveals that the signal is somewhat, but not conclusively, disfavored (1 σ –2 σ ), leading us to argue that the signal is most likely spurious. We expect that infrared photometric follow-up could more conclusively test the existence of this candidate signal, owing to the suppression of flare activity and the impressive infrared brightness of the parent star.},
doi = {10.3847/1538-3881/153/3/93},
journal = {Astronomical Journal (Online)},
number = 3,
volume = 153,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2017},
month = {Wed Mar 01 00:00:00 EST 2017}
}
  • The radial velocity-discovered exoplanet HD 97658b was recently announced to transit, with a derived planetary radius of 2.93 {+-} 0.28 R{sub Circled-Plus }. As a transiting super-Earth orbiting a bright star, this planet would make an attractive candidate for additional observations, including studies of its atmospheric properties. We present and analyze follow-up photometric observations of the HD 97658 system acquired with the Microvariability and Oscillations of STars space telescope. Our results show no transit with the depth and ephemeris reported in the announcement paper. For the same ephemeris, we rule out transits for a planet with radius larger than 2.09more » R{sub Circled-Plus }, corresponding to the reported 3{sigma} lower limit. We also report new radial velocity measurements which continue to support the existence of an exoplanet with a period of 9.5 days, and obtain improved orbital parameters.« less
  • We present a study of white-light flares from the active M5.5 dwarf Proxima Centauri using the Canadian microsatellite Microvariability and Oscillations of STars . Using 37.6 days of monitoring data from 2014 to 2015, we have detected 66 individual flare events, the largest number of white-light flares observed to date on Proxima Cen. Flare energies in our sample range from 10{sup 29} to 10{sup 31.5} erg. The flare rate is lower than that of other classic flare stars of a similar spectral type, such as UV Ceti, which may indicate Proxima Cen had a higher flare rate in its youth.more » Proxima Cen does have an unusually high flare rate given its slow rotation period, however. Extending the observed power-law occurrence distribution down to 10{sup 28} erg, we show that flares with flux amplitudes of 0.5% occur 63 times per day, while superflares with energies of 10{sup 33} erg occur ∼8 times per year. Small flares may therefore pose a great difficulty in searches for transits from the recently announced 1.27 M {sub ⊕} Proxima b, while frequent large flares could have significant impact on the planetary atmosphere.« less
  • Through photometric monitoring of the extended transit window of HD 97658b with the MOST space telescope, we have found that this exoplanet transits with an ephemeris consistent with that predicted from radial velocity measurements. The mid-transit times are 5.6{sigma} earlier than those of the unverified transit-like signals reported in 2011, and we find no connection between the two sets of events. The transit depth together with our determined stellar radius (R{sub *} = 0.703{sub -0.034}{sup +0.039} R{sub Sun }) indicates a 2.34{sup +0.18}{sub -0.15} R{sub Circled-Plus} super-Earth. When combined with the radial velocity determined mass of 7.86 {+-} 0.73 M{submore » Circled-Plus }, our radius measure allows us to derive a planet density of 3.44{sup +0.91}{sub -0.82} g cm{sup -3}. Models suggest that a planet with our measured density has a rocky core that is enveloped in an atmosphere composed of lighter elements. The star of the HD 97658 system is the second brightest known to host a transiting super-Earth, facilitating follow-up studies of this not easily daunted, warm and likely volatile-rich exoplanet.« less
  • We present photometry of two transits of the giant planet WASP-4b with a photometric precision of 400-800 parts per million and a time sampling of 25-40 s. The two midtransit times are determined to within 6 s. Together with previously published times, the data are consistent with a constant orbital period, giving no compelling evidence for period variations that would be produced by a satellite or additional planets. Analysis of the new photometry, in combination with stellar-evolutionary modeling, gives a planetary mass and radius of 1.237 {+-} 0.064 M {sub Jup} and 1.365 {+-} 0.021 R {sub Jup}, respectively. Themore » planet is 15% larger than expected based on previously published models of solar-composition giant planets. With data of the quality presented here, the detection of transits of a 'super-Earth' of radius 1.75 R {sub +} would have been possible.« less