arXiv subjects

J. McCormac

Publications and source records attributed to J. McCormac.

At least 73 records · Page 4Linked to original sources

arXiv2018

MASCARA-1 b: A hot Jupiter transiting a bright $m_V=8.3$ A-star in a misaligned orbit

We report the discovery of MASCARA-1 b, the first exoplanet discovered with the Multi-site All-Sky CAmeRA (MASCARA). It is a hot Jupiter orbiting a bright $m_V=8.3$, rapidly rotating ($v\sin i_\star > 100~\rm{km~s}^{-1}$) A8 star with a period of $2.148780\pm8\times10^{-6} ~\rm{days}$. The planet has a mass and radius of $3.7\pm0.9~\rm{M}_{\rm{Jup}}$ and $1.5\pm0.3~\rm{R}_{\rm{Jup}}$, respectively. As with most hot Jupiters transiting early-type stars we find a misalignment between the planet orbital axis and the stellar spin axis, which may be signature of the formation and migration histories of this family of planets. MASCARA-1 b has a mean density of $1.5\pm0.9~\rm{g~cm^{-3}}$ and an equilibrium temperature of $2570^{+50}_{-30}~\rm{K}$, one of the highest temperatures known for a hot Jupiter to date. The system is reminiscent of WASP-33, but the host star lacks apparent delta-scuti variations, making the planet an ideal target for atmospheric characterization. We expect this to be the first of a series of hot Jupiters transiting bright early-type stars that will be discovered by MASCARA.

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arXiv2018

MASCARA-2 b: A hot Jupiter transiting the $m_V=7.6$ A-star HD185603

In this paper we present MASCARA-2 b, a hot Jupiter transiting the $m_V=7.6$ A2 star HD 185603. Since early 2015, MASCARA has taken more than 1.6 million flux measurements of the star, corresponding to a total of almost 3000 hours of observations, revealing a periodic dimming in the flux with a depth of $1.3\%$. Photometric follow-up observations were performed with the NITES and IAC80 telescopes and spectroscopic measurements were obtained with the Hertzsprung SONG telescope. We find MASCARA-2 b orbits HD 185603 with a period of $3.474119^{+0.000005}_{-0.000006}~\rm{days}$ at a distance of $0.057 \pm 0.006~\rm{AU}$, has a radius of $1.83 \pm 0.07~\rm{R}_{\rm{J}}$ and place a $99\%$ upper limit on the mass of $< 17~\rm{M}_{\rm{J}}$. HD 185603 is a rapidly rotating early-type star with an effective temperature of $8980^{+90}_{-130}~\rm{K}$ and a mass and radius of $1.89^{+0.06}_{-0.05}~M_\odot$, $1.60 \pm 0.06~R_\odot$, respectively. Contrary to most other hot Jupiters transiting early-type stars, the projected planet orbital axis and stellar spin axis are found to be aligned with $λ=0.6 \pm 4^\circ$. The brightness of the host star and the high equilibrium temperature, $2260 \pm 50~\rm{K}$, of MASCARA-2 b make it a suitable target for atmospheric studies from the ground and space. Of particular interest is the detection of TiO, which has recently been detected in the similarly hot planets WASP-33 b and WASP-19 b.

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arXiv2017

LRG-BEASTS III: Ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80

We have performed ground-based transmission spectroscopy of the hot Jupiter orbiting the cool dwarf WASP-80 using the ACAM instrument on the William Herschel Telescope (WHT) as part of the LRG-BEASTS programme. This is the third paper of a ground-based transmission spectroscopy survey of hot Jupiters using low-resolution grism spectrographs. We observed two transits of the planet and have constructed transmission spectra spanning a wavelength range of 4640-8840A. Our transmission spectrum is inconsistent with a previously claimed detection of potassium in WASP-80b's atmosphere, and is instead most consistent with a haze. We also do not see evidence for sodium absorption at a resolution of 100A.

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arXiv2017

The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert

To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision is essential. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15 %. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31^{+0.04}_{-0.03} MJ, 1.13^{+0.03}_{-0.03} RJ, 0.22^{-0.03}_{-0.02} rhoJ and 1, 290^{+20}_{-10} K, and 0.39^{+0.02}_{-0.02} MJ, 1.55^{+0.10}_{-0.08} RJ, 0.11^{+0.02}_{-0.02} rhoJ and 1, 700^{+40}_{-40} K, respectively. Their host stars are early G type stars (with magV ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a Super-Neptune orbiting a K type star (magV = 11.6) . It has a mass of 0.128^{+0.010}_{-0.009} MJ, a radius of 0.51^{+0.02}_{-0.02} RJ, a density of 1.0^{+0.1}_{-0.1} rhoJ, an equilibrium temperature of 970^{+30}_{-20} K and an orbital period of 3.83 days. WASP-151b is slightly inflated, while WASP-153b presents a significant radius anomaly. WASP-156b, being one of the few well characterised Super-Neptunes, will help to constrain the formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms the tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behaviour for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population.

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arXiv2017

K2-110 b - a massive mini-Neptune exoplanet

We report the discovery of the exoplanet K2-110 b (previously EPIC212521166b) from K2 photometry orbiting in a 13.8637d period around an old, metal-poor K3 dwarf star. With a V-band magnitude of 11.9, K2-110 is particularly amenable to RV follow-up. A joint analysis of K2 photometry and high-precision RVs from 28 HARPS and HARPS-N spectra reveal it to have a radius of 2.6$\pm 0.1 R_{\oplus}$ and a mass of 16.7$\pm 3.2$~M$_{\oplus}$, hence a density of $5.2\pm1.2$ g.cm$^{-3}$, making it one of the most massive planets yet to be found with a sub-Neptune radius. When accounting for compression, the resulting Earth-like density is best fitted by a 0.2 M$_{\oplus}$ hydrogen atmosphere over an 16.5 M$_{\oplus}$ Earth-like interior, although the planet could also have significant water content. At 0.1~AU, even taking into account the old stellar age of $8 \pm 3$ Gyr, the planet is unlikely to have been significantly affected by EUV evaporation. However the planet likely disc-migrated to its current position making the lack of a thick H$_2$ atmosphere puzzling. This analysis has made K2-110 b one of the best-characterised mini-Neptunes with density constrained to less than 30%.

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arXiv2017

Rayleigh scattering in the transmission spectrum of HAT-P-18b

We have performed ground-based transmission spectroscopy of the hot Jupiter HAT-P-18b using the ACAM instrument on the William Herschel Telescope (WHT). Differential spectroscopy over an entire night was carried out at a resolution of $R \approx 400$ using a nearby comparison star. We detect a bluewards slope extending across our optical transmission spectrum which runs from 4750 to 9250Å. The slope is consistent with Rayleigh scattering at the equilibrium temperature of the planet (852K). We do not detect enhanced sodium absorption, which indicates that a high-altitude haze is masking the feature and giving rise to the Rayleigh slope. This is only the second discovery of a Rayleigh scattering slope in a hot Jupiter atmosphere from the ground, and our study illustrates how ground-based observations can provide transmission spectra with precision comparable to the Hubble Space Telescope.

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arXiv2016

WASP-86b and WASP-102b: super-dense versus bloated planets

We report the discovery of two transiting planetary systems: a super dense, sub-Jupiter mass planet WASP-86b (\mpl\ = 0.82 $\pm$ 0.06 \mj, \rpl\ = 0.63 $\pm$ 0.01 \rj), and a bloated, Saturn-like planet WASP-102b (\mpl\ = 0.62 $\pm$ 0.04 \mj, \rpl\=1.27 $\pm$ 0.03 \rj). They orbit their host star every $\sim$5.03, and $\sim$2.71 days, respectively. The planet hosting WASP-86 is a F7 star (\teff\ = 6330$\pm$110 K, \feh\ = $+$0.23 $\pm$ 0.14 dex, and age $\sim$0.8--1~Gyr), WASP-102 is a G0 star (\teff\ = 5940$\pm$140 K, \feh\ = $-$0.09$\pm$ 0.19 dex, and age $\sim$1~Gyr). These two systems highlight the diversity of planetary radii over similar masses for giant planets with masses between Saturn and Jupiter. WASP-102b shows a larger than model-predicted radius, indicating that the planet is receiving a strong incident flux which contributes to the inflation of its radius. On the other hand, with a density of $ρ_{pl}$ = 3.24$\pm$~0.3~$ρ_{jup}$, WASP-86b is the densest gas giant planet among planets with masses in the range 0.05 $<M$_{pl}$<$ 2.0 \mj. With a stellar mass of 1.34 M$_{\odot}$ and \feh = $+$0.23 dex, WASP-86 could host additional massive and dense planets given that its protoplanetary disc is expected to also have been enriched with heavy elements. In order to match WASP-86b's density, an extrapolation of theoretical models predicts a planet composition of more than 80\% in heavy elements (whether confined in a core or mixed in the envelope). This fraction corresponds to a core mass of approximately 210\me\ for WASP-86b's mass of \mpl$\sim$260\,\me. Only planets with masses larger than about 2\mj\ have larger densities than that of WASP-86b, making it exceptional in its mass range.

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arXiv2016

Discovery of WASP-113b and WASP-114b, two inflated hot-Jupiters with contrasting densities

We present the discovery and characterisation of the exoplanets WASP-113b and WASP-114b by the WASP survey, {\it SOPHIE} and {\it CORALIE}. The planetary nature of the systems was established by performing follow-up photometric and spectroscopic observations. The follow-up data were combined with the WASP-photometry and analysed with an MCMC code to obtain system parameters. The host stars WASP-113 and WASP-114 are very similar. They are both early G-type stars with an effective temperature of $\sim 5900\,$K, [Fe/H]$\sim 0.12$ and $T_{\rm eff}$ $\sim 4.1$dex. However, WASP-113 is older than WASP-114. Although the planetary companions have similar radii, WASP-114b is almost 4 times heavier than WASP-113b. WASP-113b has a mass of $0.48\,$ $\mathrm{M}_{\rm Jup}$ and an orbital period of $\sim 4.5\,$days; WASP-114b has a mass of $1.77\,$ $\mathrm{M}_{\rm Jup}$ and an orbital period of $\sim 1.5\,$days. Both planets have inflated radii, in particular WASP-113 with a radius anomaly of $\Re=0.35$. The high scale height of WASP-113b ($\sim 950$ km ) makes it a good target for follow-up atmospheric observations.

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arXiv2016

WASP-92b, WASP-93b and WASP-118b: Three new transiting close-in giant planets

We present the discovery of three new transiting giant planets, first detected with the WASP telescopes, and establish their planetary nature with follow up spectroscopy and ground-based photometric lightcurves. WASP-92 is an F7 star, with a moderately inflated planet orbiting with a period of 2.17 days, which has $R_p = 1.461 \pm 0.077 R_{\rm J}$ and $M_p = 0.805 \pm 0.068 M_{\rm J}$. WASP-93b orbits its F4 host star every 2.73 days and has $R_p = 1.597 \pm 0.077 R_{\rm J}$ and $M_p = 1.47 \pm 0.029 M_{\rm J}$. WASP-118b also has a hot host star (F6) and is moderately inflated, where $R_p = 1.440 \pm 0.036 R_{\rm J}$ and $M_p = 0.513 \pm 0.041 M_{\rm J}$ and the planet has an orbital period of 4.05 days. They are bright targets (V = 13.18, 10.97 and 11.07 respectively) ideal for further characterisation work, particularly WASP-118b, which is being observed by K2 as part of campaign 8. WASP-93b is expected to be tidally migrating outwards, which is divergent from the tidal behaviour of the majority of hot Jupiters discovered.

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arXiv2016

Supernova 2014J at M82: II. Direct Analysis of Spectra Obtained with Isaac Newton and William Herschel Telescopes

We analyze a time series of optical spectra of SN~2014J from almost two weeks prior to maximum to nearly four months after maximum. We perform our analysis using the SYNOW code, which is well suited to track the distribution of the ions with velocity in the ejecta. We show that almost all of the spectral features during the entire epoch can be identified with permitted transitions of the common ions found in normal SNe Ia in agreement with previous studies. We show that 2014J is a relatively normal SN Ia. At early times the spectral features are dominated by Si II, S II, Mg II, and Ca II. These ions persist to maximum light with the appearance of Na I and Mg I. At later times iron-group elements also appear, as expected in the stratified abundance model of the formation of normal type Ia SNe. We do not find significant spectroscopic evidence for oxygen, until 100 days after maximum light. The +100 day identification of oxygen is tentative, and would imply significant mixing of unburned or only slight processed elements down to a velocity of 6,000 km/s. Our results are in relatively good agreement with other analyses in the IR. We briefly compare SN 2011fe to SN 2014J and conclude that the differences could be due to different central densities at ignition or differences in the C/O ratio of the progenitors.

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arXiv2016

K2-30b and K2-34b: two inflated hot-Jupiters around Solar-type stars

We report the discovery of the two hot-Jupiters K2-30b and K2-34b. The two planets were detected transiting their main-sequence star with periods $\sim$ 4.099 and $\sim$ 2.996 days, in campaigns 4 and 5 of the extension of the Kepler mission, K2. Subsequent ground-based radial velocity follow-up with SOPHIE, HARPS-N and CAFE, established the planetary nature of the transiting objects. We analyzed the transit signal, radial velocity and spectral energy distributions of the two systems to characterize their properties. Both planets (K2-30b and K2-34b) are bloated hot-Jupiters (1.25 $R_{\rm Jup}$ and 1.33 $R_{\rm Jup}$) around relatively bright (V =13.5 and V=11.5), slow rotating main-sequence (G8 and F9) stars. Thus, these systems are good candidates for detecting the Rossiter-MacLaughlin effect to measure their obliquity and for atmospheric studies.

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arXiv2016

EPIC211089792 b: an aligned and inflated hot jupiter in a young visual binary

In the present paper we report the discovery of a new hot Jupiter, EPIC211089792 b, first detected by the Super-WASP observatory and then by the K2 space mission during its campaign 4. The planet has a period of 3.25d, a mass of 0.73 +/- 0.04 Mjup, and a radius of 1.19 +/- 0.02 Rjup. The host star is a relatively bright (V=12.5) G7 dwarf with a nearby K5V companion. Based on stellar rotation and the abundance of Lithium, we find that the system might be as young as about 450 Myr. The observation of the Rossiter-McLaughlin effect shows the planet is aligned with respect to the stellar spin. Given the deep transit (20mmag), the magnitude of the star and the presence of a nearby stellar companion, the planet is a good target for both space- and ground-based transmission spectroscopy, in particular in the near-infrared where the both stars are relatively bright.

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arXiv2016

K2 Variable Catalogue II: Machine Learning Classification of Variable Stars and Eclipsing Binaries in K2 Fields 0-4

We are entering an era of unprecedented quantities of data from current and planned survey telescopes. To maximise the potential of such surveys, automated data analysis techniques are required. Here we implement a new methodology for variable star classification, through the combination of Kohonen Self Organising Maps (SOM, an unsupervised machine learning algorithm) and the more common Random Forest (RF) supervised machine learning technique. We apply this method to data from the K2 mission fields 0-4, finding 154 ab-type RR Lyraes (10 newly discovered), 377 Delta Scuti pulsators, 133 Gamma Doradus pulsators, 183 detached eclipsing binaries, 290 semi-detached or contact eclipsing binaries and 9399 other periodic (mostly spot-modulated) sources, once class significance cuts are taken into account. We present lightcurve features for all K2 stellar targets, including their three strongest detected frequencies, which can be used to study stellar rotation periods where the observed variability arises from spot modulation. The resulting catalogue of variable stars, classes, and associated data features are made available online. We publish our SOM code in Python as part of the open source PyMVPA package, which in combination with already available RF modules can be easily used to recreate the method.

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arXiv2016

SN 2014J at M82: I. A middle-class type Ia supernova by all spectroscopic metrics

We present the intensive spectroscopic follow up of the type Ia supernova (SN Ia) 2014J in the starburst galaxy M82. Twenty-seven optical spectra have been acquired from January 22nd to September 1st 2014 with the Isaac Newton (INT) and William Herschel (WHT) Telescopes. After correcting the observations for the recession velocity of M82 and for Milky Way and host galaxy extinction, we measured expansion velocities from spectral line blueshifts and pseudo-equivalent width of the strongest features in the spectra, which gives an idea on how elements are distributed within the ejecta. We position SN 2014J in the Benetti (2005), Branch et al. (2006) and Wang et al. (2009) diagrams. These diagrams are based on properties of the Si II features and provide dynamical and chemical information about the SN ejecta. The nearby SN 2011fe, which showed little evidence for reddening in its host galaxy, is shown as a reference for comparisons. SN 2014J is a border-line object between the Core-normal (CN) and Broad-line (BL) groups, which corresponds to an intermediate position between Low Velocity Gradient (LVG) and High Velocity Gradient (HVG) objects. SN 2014J follows the R(Si II)-Δm15 correlation, which confirms its classification as a relatively normal SN Ia. Our description of the SN Ia in terms of the evolution of the pseudo-equivalent width of various ions as well as the position in the various diagrams put this specific SN Ia into the overall sample of SN Ia.

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arXiv2015

Single Transit Candidates from K2: Detection and Period Estimation

Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool ("Namaste: An Mcmc Analysis of Single Transit Exoplanets") to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to 7 candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of $540 ^{+410}_{-230}$ days and a radius of $0.51 \pm 0.05 R_{Jup}$. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia.

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arXiv2015

Photo-dynamical mass determination of the multi-planetary system K2-19

K2-19 is the second multi-planetary system discovered with K2 observations. The system is composed of two Neptune size planets close to the 3:2 mean-motion resonance. To better characterise the system we obtained two additional transit observations of K2-19b and five additional radial velocity observations. These were combined with K2 data and fitted simultaneously with the system dynamics (photo-dynamical model) which increases the precision of the transit time measurements. The higher transit time precision allows us to detect the chopping signal of the dynamic interaction of the planets that in turn permits to uniquely characterise the system. Although the reflex motion of the star was not detected, dynamic modelling of the system allowed us to derive planetary masses of $M_b= 44 \pm 12\, M_{\oplus}$ and $M_c = 15.9 \pm 7.0\, M_{\oplus}$ for the inner and the outer planets respectively, leading to densities close to Uranus. We also show that our method allows the derivation of mass ratios using only the 80 days of observations during the first campaign of K2.

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arXiv2015

K2 Variable Catalogue: Variable Stars and Eclipsing Binaries in K2 Campaigns 1 and 0

We have created a catalogue of variable stars found from a search of the publicly available K2 mission data from Campaigns 1 and 0. This catalogue provides the identifiers of 8395 variable stars, including 199 candidate eclipsing binaries with periods up to 60d and 3871 periodic or quasi-periodic objects, with periods up to 20d for Campaign 1 and 15d for Campaign 0. Lightcurves are extracted and detrended from the available data. These are searched using a combination of algorithmic and human classification, leading to a classifier for each object as an eclipsing binary, sinusoidal periodic, quasi periodic, or aperiodic variable. The source of the variability is not identified, but could arise in the non-eclipsing binary cases from pulsation or stellar activity. Each object is cross-matched against variable star related guest observer proposals to the K2 mission, which specifies the variable type in some cases. The detrended lightcurves are also compared to lightcurves currently publicly available. The resulting catalogue is made available online via the MAST archive at https://archive.stsci.edu/prepds/k2varcat/, and gives the ID, type, period, semi-amplitude and range of the variation seen. We also make available the detrended lightcurves for each object.

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arXiv2014

Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation

High resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652\,Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over 6 pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least two at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km/s (depending how measured) and at least ten times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 km/s on a timescale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra.

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