Dr. David Brown
Research Fellow, Physics - Astronomy | University of Warwick
Coventry, UNITED KINGDOM
David Brown researches the discovery of extra-solar planets, the evolution of planetary systems, and tides on extra-solar planets.
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Areas of Expertise (6)
Astronomy
Satellites and Space Telescopes
Exoplanet Atmospheres
Exoplanet Discoveries
Exomoons
General Astronomy and Astrophysics
Education (2)
University of St. Andrews: Ph.D., Astronomy and Astrophysics 2013
University of Warwick: M.Phys., Physics 2009
Links (1)
Selected Media Appearances (1)
The search for a new earth Everything you ever wanted to know about the galaxy's mysterious 'exo-planets'
The Herald Scotland online
2016-05-14
As Dr David Brown of the University of Warwick, an exoplanet scientist working on the project puts it: “PLATO has been designed specifically to find rocky earth-like planets that could have liquid water, around stars like the sun. That is what excites me. That is one of the things I would love to see finally happen. It is only a matter of time. We’re so close at the moment that I want to say sooner than ten years.”
Selected Articles (5)
Rossiter-McLaughlin models and their effect on estimates of stellar rotation, illustrated using six WASP systems
Monthly Notices of the Royal Astronomical Society
2017 We present new measurements of the projected spin-orbit angle λ for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses of previously measured systems using new data (WASP-71, and -79). We use three different models based on two different techniques: radial velocity measurements of the Rossiter-McLaughlin effect, and Doppler tomography. Our comparison of the different models reveals that they produce projected stellar rotation velocities (v sin Is) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Boué model for the Rossiter-McLaughlin effect consistently underestimates the value of v sin Is compared to the Hirano model. Although v sin Is differed, the effect on λ was small for our sample, with all three methods producing values in agreement with each other. Using Doppler tomography, we find that WASP-61 b (λ =4.0°^{+17.1}_{-18.4}), WASP-71 b (λ =-1.9°^{+7.1}_{-7.5}), and WASP-78 b (λ = -6.4° ± 5.9) are aligned. WASP-62 b (λ =19.4°^{+5.1}_{ -4.9}) is found to be slightly misaligned, while WASP-79 b (λ =-95.2°^{+0.9}_{ -1.0}) is confirmed to be strongly misaligned and has a retrograde orbit. We explore a range of possibilities for the orbit of WASP-76 b, finding that the orbit is likely to be strongly misaligned in the positive λ direction.
Three transiting planet discoveries from the Wide Angle Search for Planets: WASP-85 A b; WASP-116 b, and WASP-149 b
Monthly Notices of the Royal Astronomical Society
2014 We report the discovery of three new transiting planets: WASP-85 A b, WASP-116 b, and WASP-149 b. WASP-85 b orbits its host star every 2.66 days, and has a mass of 1.25 M_Jup and a radius of 1.25 R_Jup. The host star is of G5 spectral type, with magnitude V = 11.2, and lies 141 pc distant. The system has a K-dwarf binary companion, WASP-85 B, at a separation of ~1.5". The close proximity of this companion leads to contamination of our photometry, decreasing the apparent transit depth that we account for during our analysis. Analysis of the Ca II H+K lines shows strong emission that implies that both binary components are strongly active. WASP-116 b is a warm, mildly inflated super-Saturn, with a mass of 0.59 M_Jup and a radius of 1.43 R_Jup. It was discovered orbiting a metal-poor ([Fe/H] = -0.28 dex), cool (T_eff = 5950 K) G0 dwarf every 6.61 days. WASP-149 b is a typical hot Jupiter, orbiting a G6 dwarf with a period of 1.33 days. The planet has a mass and radius of 1.05 M_Jup and 1.29 R_Jup, respectively. The stellar host has an effective temperature of T_eff = 5750 K and has a metallicity of [Fe/H] = 0.16 dex. WASP photometry of the system is contaminated by a nearby star; we therefore corrected the depth of the WASP transits using the measured dilution. WASP-149 lies inside the 'Neptune desert' identified in the planetary mass-period plane by Mazeh, Holczer & Faigler (2016). We model the modulation visible in the K2 lightcurve of WASP-85 using a simple three-spot model consisting of two large spots on WASP-85 A, and one large spot on WASP-85 B, finding rotation periods of 13.1+/-0.1 days for WASP-85 A and 7.5+/-0.03 days for WASP-85 B. We estimate stellar inclinations of I_A = 66.8+/-0.7 degrees and I_B = 39.7+/-0.2 degrees, and constrain the obliquity of WASP-85 A b to be psi
Discrepancies between isochrone fitting and gyrochronology for exoplanet host stars?
Monthly Notices of the Royal Astronomical Society
2014 Using a sample of 68 planet-hosting stars, I carry out a comparison of isochrone fitting and gyrochronology to investigate whether tidal interactions between the stars and their planets are leading to underestimated ages using the latter method. I find a slight tendency for isochrones to produce older age estimates but find no correlation with tidal time-scale, although for some individual systems the effect of tides might be leading to more rapid rotation than expected from the stars' isochronal age, and therefore an underestimated gyrochronology age. By comparing to planetary systems in stellar clusters, I also find that in some cases isochrone fitting can overestimate the age of the star. The evidence for any bias on a sample-wide level is inconclusive. I also consider the subset of my sample for which the sky-projected alignment angle between the stellar rotation axis and the planet's orbital axis has been measured, finding similar patterns to those identified in the full sample. However, small sample sizes for both the misaligned and aligned systems prevent strong conclusions from being drawn.
Analysis of Spin-Orbit Alignment in the WASP-32, WASP-38, and HAT-P-27/WASP-40 Systems
The Astrophysical Journal
2012 We present measurements of the spin-orbit alignment angle, λ, for the hot Jupiter systems WASP-32, WASP-38, and HAT-P-27/WASP-40, based on data obtained using the HARPS spectrograph. We analyze the Rossiter-McLaughlin effect for all three systems and also carry out Doppler tomography for WASP-32 and WASP-38. We find that WASP-32 (T eff = 6140+90 - 100 K) is aligned, with an alignment angle of λ = 10fdg5 + 6.4 - 6.5 obtained through tomography, and that WASP-38 (T eff = 6180+40 - 60 K) is also aligned, with tomographic analysis yielding λ = 7fdg5 + 4.7 - 6.1. The latter result provides an order-of-magnitude improvement in the uncertainty in λ compared to the previous analysis of Simpson et al. We are only able to loosely constrain the angle for HAT-P-27/WASP-40 (T eff = 5190+160 - 170 K) to λ = 24fdg2 + 76.0 - 44.5, owing to the poor signal-to-noise ratio of our data. We consider this result a non-detection under a slightly updated version of the alignment test of Brown et al. We place our results in the context of the full sample of spin-orbit alignment measurements, finding that they provide further support for previously established trends. Based on observations (under proposal 087.C-0649) made using the HARPS High Resolution Échelle Spectrograph mounted on the ESO 3.6 m at the ESO La Silla observatory.
Rossiter-McLaughlin effect measurements for WASP-16, WASP-25 and WASP-31
Monthly Notices of the Royal Astronomical Society
2012 We present new measurements of the Rossiter-McLaughlin (RM) effect for three Wide Angle Search for transiting Planets (WASP) planetary systems, WASP-16, WASP-25 and WASP-31, from a combined analysis of their complete sets of photometric and spectroscopic data. We find a low-amplitude RM effect for WASP-16 (Teff= 5700 ± 150 K), suggesting that the star is a slow rotator and thus of an advanced age, and obtain a projected alignment angle of ?. For WASP-25 (Teff= 5750 ± 100 K), we detect a projected spin-orbit angle of λ= 14°.6 ± 6°.7. WASP-31 (Teff= 6300 ± 100 K) is found to be well aligned, with a projected spin-orbit angle of λ= 2°.8 ± 3°.1. A circular orbit is consistent with the data for all three systems, in agreement with their respective discovery papers. We consider the results for these systems in the context of the ensemble of RM measurements made to date. We find that whilst WASP-16 fits the hypothesis of Winn et al. that ‘cool’ stars (Teff < 6250 K) are preferentially aligned, WASP-31 has little impact on the proposed trend. We bring the total distribution of the true spin-orbit alignment angle, ψ, up to date, noting that recent results have improved the agreement with the theory of Fabrycky & Tremaine at mid-range angles. We also suggest a new test for judging misalignment using the Bayesian information criterion, according to which WASP-25 b’s orbit should be considered to be aligned. Based on observations made using the CORALIE high-resolution echelle spectrograph mounted on the 1.2-m Euler Swiss Telescope and the HARPS high-resolution echelle spectrograph mounted on the ESO 3.6-m (under proposals 084.C-0185 and 085.C-0393), both at the ESO La Silla observatory.
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