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A. J. Norton

Publications and source records attributed to A. J. Norton.

At least 19 recordsLinked to original sources
arXiv2024

4XMM~J182531.5$-$144036: A new persistent Be/X-ray binary found within the \emph{XMM-Newton} serendipitous survey

We aim to investigate the nature of time-variable X-ray sources detected in the {\it XMM-Newton} serendipitous survey. The X-ray light curves of objects in the {\it XMM-Newton} serendipitous survey were searched for variability and coincident serendipitous sources observed by {\it Chandra} were also investigated. Subsequent infrared spectroscopy of the counterparts to the X-ray objects that were identified using UKIDSS was carried out using {\it ISAAC} on the VLT. We found that the object 4XMM~J182531.5--144036 detected in the {\it XMM-Newton} serendipitous survey in April 2008 was also detected by {\it Chandra} as CXOU~J182531.4--144036 in July 2004. Both observations reveal a hard X-ray source displaying a coherent X-ray pulsation at a period of 781~s. The source position is coincident with a $K=14$ mag infrared object whose spectrum exhibits strong HeI and Br$γ$ emission lines and an infrared excess above that of early B-type dwarf or giant stars. We conclude that 4XMM~J182531.5--144036 is a Be/X-ray binary pulsar exhibiting persistent X-ray emission and is likely in a long period, low eccentricity orbit, similar to X Per.

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arXiv2020

Gaia18aen: First symbiotic star discovered by Gaia

Besides the astrometric mission of the Gaia satellite, its repeated and high-precision measurements serve also as an all-sky photometric transient survey. The sudden brightenings of the sources are published as Gaia Photometric Science Alerts and are made publicly available allowing the community to photometrically and spectroscopically follow-up the object. The goal of this paper was to analyze the nature and derive the basic parameters of Gaia18aen, transient detected at the beginning of 2018. It coincides with the position of the emission line star WRAY 15-136. The brightening was classified as a "nova?" on the basis of subsequent spectroscopic observation. We have analyzed two spectra of Gaia18aen and collected the available photometry of the object covering the brightenings in 2018 and also the preceding and following periods of quiescence. Based on this observational data, we have derived the parameters of Gaia18aen and discussed the nature of the object. Gaia18aen is the first symbiotic star discovered by the Gaia satellite. The system is an S-type symbiotic star and consists of an M giant of a slightly super-solar metallicity, with Teff ~3500 K, a radius of ~230 R$\odot$, and a high luminosity L ~7400 L$\odot$. The hot component is a hot white dwarf. We tentatively determined the orbital period of the system ~487 days. The main outburst of Gaia18aen in 2018 was accompanied by a decrease in the temperature of the hot component. The first phase of the outburst was characterized by the high luminosity L ~27000 L$\odot$, which remained constant for about three weeks after the optical maximum, later followed by the gradual decline of luminosity and increase of temperature. Several re-brightenings have been detected on the timescales of hundreds of days.

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arXiv2020

Monitoring of transiting exoplanets and their host stars with small aperture telescopes

Exoplanet research is now target rich with a wide diversity of systems making it difficult for high demand observatories to undertake follow up observations over extended periods of time. We investigate the effectiveness of using 0.4m-class telescopes for monitoring transiting hot Jupiters and their host stars. We consider two representative case studies: WASP-52b with 13 new transits, and HAT-P-23b with 17 new transits and concurrent photometric monitoring covering 78 days. We present updated system parameters and combine our new transit times with previously published results to calculate new ephemerides for both systems. Our analysis of transit mid-times for WASP-52b results in a slight preference for a quadratic ephemeris ($Δχ_ν^2 = 0.07$, $ΔBIC = 1.53$ over a linear ephemeris. We discuss the reality of this quadratic ephemeris indicating a period change of $ δP / δt = -38.6\pm4{\rm ms~yr^{-1}}$ and consider possible causes. WASP-52 is known to be an active star with previous publications reporting many spot crossing events, however no such events are seen in our new photometry. Our analysis shows that WASP-52 is still active and that the latitude of the spots has likely migrated away from the transit chord. We confirm the inflated nature and circular orbit for HAT-P-23b. Our monitoring of HAT-P-23 reveals a periodicity of 7.015 days with an amplitude of 0.011 mag which we interpret as the rotation period of HAT-P-23. The photometric and transit timing precision achieved in the case studies shows that this class of telescope is capable of precise characterisation and long-term monitoring of transiting hot Jupiters in support of dedicated ongoing and future ground and space based observations.

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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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arXiv2016

Pulsation versus metallicism in Am stars as revealed by LAMOST and WASP

We present the results of a study of a large sample of A and Am stars with spectral types from LAMOST and light curves from WASP. We find that, unlike normal A stars, $δ$ Sct pulsations in Am stars are mostly confined to the effective temperature range 6900 $<$ $T_{\rm eff}$ $<$ 7600 K. We find evidence that the incidence of pulsations in Am stars decreases with increasing metallicism (degree of chemical peculiarity). The maximum amplitude of the pulsations in Am stars does not appear to vary significantly with metallicism. The amplitude distributions of the principal pulsation frequencies for both A and Am stars appear very similar and agree with results obtained from Kepler photometry. We present evidence that suggests turbulent pressure is the main driving mechanism in pulsating Am stars, rather than the $κ$-mechanism, which is expected to be suppressed by gravitational settling in these stars.

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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

The mass of the black hole in LMC X-3

New high resolution, optical spectroscopy of the high mass X-ray binary LMC X-3, shows the spectral type of the donor star changes with phase due to irradiation by the X-ray source. We find the spectral type is likely to be B5V, and only appears as B3V when viewing the heated side of the donor. Combining our measurements with those previously published, and taking into account the effects of X-ray irradiation, results in a value for the donor star radial velocity semi-amplitude of 256.7 +/- 4.9 km/s. We find the mass of the black hole lies in the range 9.5 - 13.6 solar masses.

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arXiv2016

SuperWASP discovery and SALT confirmation of a semi-detached eclipsing binary that contains a delta Scuti star

We searched the SuperWASP archive for objects displaying multiply periodic photometric variations. Specifically we sought evidence for eclipsing binary stars displaying a further non-harmonically related signal in their power spectra. The object SWASP J050634.16-353648.4 is identified as a relatively bright (V ~ 11.5) semi-detached eclipsing binary with a 5.104 d orbital period that displays coherent pulsations with a semi-amplitude of 65 mmag at a frequency of 13.45 per day. Follow-up radial velocity spectroscopy with the Southern African Large Telescope confirmed the binary nature of the system. Using the phoebe code to model the radial velocity curve with the SuperWASP photometry allowed parameters of both stellar components to be determined. This yielded a primary (pulsating) star with a mass of 1.73 +/- 0.11 solar mass and a radius of 2.41 +/- 0.06 solar radii plus a Roche-lobe filling secondary star with a mass of 0.41 +/- 0.03 solar mass and a radius of 4.21 +/- 0.11 solar radii. 1SWASP J050634.16-353648.4 is therefore a bright delta Sct pulsator in a semi-detached eclipsing binary with one of the largest pulsation amplitudes of any such system known. The pulsation constant indicates that the mode is likely a first overtone radial pulsation.

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arXiv2015

Orbital period changes and the higher-order multiplicity fraction amongst SuperWASP eclipsing binaries

Orbital period changes of binary stars may be caused by the presence of a third massive body in the system. Here we have searched the archive of the Wide Angle Search for Planets (SuperWASP) project for evidence of period variations in 13927 eclipsing binary candidates. Sinusoidal period changes, strongly suggestive of third bodies, were detected in 2% of cases; however, linear period changes were observed in a further 22% of systems. We argue on distributional grounds that the majority of these apparently linear changes are likely to reflect longer-term sinusoidal period variations caused by third bodies, and thus estimate a higher-order multiplicity fraction of 24% for SuperWASP binaries, in good agreement with other recent figures for the fraction of triple systems amongst binary stars in general.

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arXiv2015

The doubly eclipsing quintuple low-mass star system 1SWASP J093010.78+533859.5

Our discovery of 1SWASP J093010.78+533859.5 as a probable doubly eclipsing quadruple system containing a contact binary with P~0.23 d and a detached binary with P~1.31 d was announced in 2013. Subsequently Koo et al. confirmed the detached binary spectroscopically and identified a fifth set of static spectral lines at its location, corresponding to a further non-eclipsing component of the system. Here we present new spectroscopic and photometric observations, allowing confirmation of the contact binary and improved modelling of all four eclipsing components. The detached binary is found to contain components of masses 0.837(8) and 0.674(7) M_sol, with radii of 0.832(18) and 0.669(18) R_sol and effective temperatures of 5185(-20,+25) and 4325(-15,+20) K respectively, the contact system has masses 0.86(2) and 0.341(11) M_sol, radii of 0.79(4) and 0.52(5) R_sol respectively, and a common T_eff of 4700(50) K. The fifth star is of similar temperature and spectral type to the primaries in the two binaries. Long-term photometric observations indicate the presence of a spot on one component of the detached binary, moving at an apparent rate of approximately one rotation every two years. Both binaries have consistent system velocities around -11 to -12 km/s, which match the average radial velocity of the fifth star, consistent distance estimates for both subsystems of d=78(3) and d=73(4) pc are also found, and (with some further assumptions) of d=83(9) pc for the fifth star. These findings strongly support the claim that both binaries (and very probably all five stars) are gravitationally bound in a single system. The consistent angles of inclination found for the two binaries (88.2(3) and 86(4) degrees) may also indicate that they originally formed by fragmentation (~9-10 Gyr ago) from a single protostellar disk and subsequently remained in the same orbital plane.

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arXiv2014

Period and amplitude variations in post-common-envelope eclipsing binaries observed with SuperWASP

Period or amplitude variations in eclipsing binaries may reveal the presence of additional massive bodies in the system, such as circumbinary planets. Here, we have studied twelve previously-known eclipsing post-common-envelope binaries for evidence of such light curve variations, on the basis of multi-year observations in the SuperWASP archive. The results for HW Vir provided strong evidence for period changes consistent with those measured by previous studies, and help support a two-planet model for the system. ASAS J102322-3737.0 exhibited plausible evidence for a period increase not previously suggested; while NY Vir, QS Vir and NSVS 14256825 afforded less significant support for period change, providing some confirmation to earlier claims. In other cases, period change was not convincingly observed; for AA Dor and NSVS 07826147, previous findings of constant period were confirmed. This study allows us to present hundreds of new primary eclipse timings for these systems, and further demonstrates the value of wide-field high-cadence surveys like SuperWASP for the investigation of variable stars.

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arXiv2014

A Window on Exoplanet Dynamical Histories: Rossiter-McLaughlin Observations of WASP-13b and WASP-32b

We present Rossiter-McLaughlin observations of WASP-13b and WASP-32b and determine the sky-projected angle between the normal of the planetary orbit and the stellar rotation axis ($λ$). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of $λ={8^{\circ}}^{+13}_{-12}$ and $λ={-2^{\circ}}^{+17}_{-19}$, respectively. Both WASP-13 and WASP-32 have $T_{\mathrm{eff}}<6250$K and therefore these systems support the general trend that aligned planetary systems are preferentially found orbiting cool host stars. A Lomb-Scargle periodogram analysis was carried out on archival SuperWASP data for both systems. A statistically significant stellar rotation period detection (above 99.9\% confidence) was identified for the WASP-32 system with $P_{\mathrm{rot}}=11.6 \pm 1.0 $ days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, $R_{\star}$, and $v \sin i$ if a stellar inclination of $i_{\star}=90^{\circ}$ is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, $ψ$, was found to be $ψ=11^{\circ} \pm 14$. We conclude with a discussion on the alignment of systems around cool host stars with $T_{\mathrm{eff}}<6150$K by calculating the tidal dissipation timescale. We find that systems with short tidal dissipation timescales are preferentially aligned and systems with long tidal dissipation timescales have a broad range of obliquities.

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arXiv2014

On the incidence of eclipsing Am binary systems in the SuperWASP survey

The results of a search for eclipsing Am star binaries using photometry from the SuperWASP survey are presented. The light curves of 1742 Am stars fainter than V = 8.0 were analysed for the presences of eclipses. A total of 70 stars were found to exhibit eclipses, with 66 having sufficient observations to enable orbital periods to be determined and 28 of which are newly identified eclipsing systems. Also presented are spectroscopic orbits for 5 of the systems. The number of systems and the period distribution is found to be consistent with that identified in previous radial velocity surveys of `classical' Am stars.

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arXiv2014

Parameters of two low-mass contact eclipsing binaries near the short-period limit

The two objects 1SWASP J150822.80-054236.9 and 1SWASP J160156.04+202821.6 were initially detected from their SuperWASP archived light curves as candidate eclipsing binaries with periods close to the short-period cut-off of the orbital period distribution of main sequence binaries, at ~0.2 d. Here, using INT spectroscopic data, we confirm them as double-lined spectroscopic and eclipsing binaries, in contact configuration. Following modelling of their visual light curves and radial velocity curves, we determine their component and system parameters to precisions between ~2 and 11%. The former system contains 1.07 and 0.55 M_sun components, with radii of 0.90 and 0.68 R_sun respectively; its primary exhibits pulsations with period 1/6 the orbital period of the system. The latter contains 0.86 and 0.57 M_sun components, with radii of 0.75 and 0.63R_sun respectively.

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arXiv2014

High frequency A-type pulsators discovered using SuperWASP

We present the results of a survey using the WASP archive to search for high frequency pulsations in F-, A- and B-type stars. Over 1.5 million targets have been searched for pulsations with amplitudes greater than 0.5 millimagnitude. We identify over 350 stars which pulsate with periods less than 30 min. Spectroscopic follow-up of selected targets has enabled us to confirm 10 new rapidly oscillating Ap stars, 13 pulsating Am stars and the fastest known $δ$ Scuti star. We also observe stars which show pulsations in both the high-frequency domain and in the low-frequency $δ$ Scuti range. This work shows the power of the WASP photometric survey to find variable stars with amplitudes well below the nominal photometric precision per observation.

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arXiv2013

Astrophysical parameters of the peculiar X-ray transient IGR J11215-5952

The hard X-ray source IGR J11215-5952 is a peculiar transient, displaying very short X-ray outbursts every 165 days. We obtained high-resolution spectra of the optical counterpart, HD 306414, at different epochs, spanning a total of three months, before and around the 2007 February outburst with the combined aims of deriving its astrophysical parameters and searching for orbital modulation. We fit model atmospheres generated with the fastwind code to the spectrum. We also cross-correlated each individual spectrum to the best-fit model to derive radial velocities. From its spectral features, we classify HD 306414 as B0.5 Ia. From the model fit, we find Teff = 24 700 K and log g = 2.7, in good agreement with the morphological classification. Using the interstellar lines in its spectrum, we estimate a distance to HD 306414 d > 7 kpc. Assuming this distance, we derive R* = 40 Rsol and Mspect = 30 Msol (consistent, within errors, with Mevol = 38 Msol). Radial velocity changes are not dominated by the orbital motion, and we find an upper limit on the semi-amplitude for the optical component Kopt < 11 +- 6 km/s. Large variations in the depth and shape of photospheric lines suggest the presence of strong pulsations, which may be the main cause of the radial velocity changes. Very significant variations, uncorrelated with those of the photospheric lines are seen in the shape and position of the Halpha emission feature around the time of the X-ray outburst, but large excursions are also observed at other times. HD 306414 is a normal B0.5 Ia supergiant. Its radial velocity curve is dominated by an effect that is different from binary motion, and is most likely stellar pulsations. The data available suggest that the X-ray outbursts are caused by the close passage of the neutron star in a very eccentric orbit, perhaps leading to localised mass outflow. (abridged).

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arXiv2013

Discovery of WASP-65b and WASP-75b: Two Hot Jupiters Without Highly Inflated Radii

We report the discovery of two transiting hot Jupiters, WASP-65b (M_pl = 1.55 +/- 0.16 M_J; R_pl = 1.11 +/- 0.06 R_J), and WASP-75b (M_pl = 1.07 +/- 0.05 M_J; R_pl = 1.27 +/- 0.05 R_J). They orbit their host star every 2.311, and 2.484 days, respectively. The planet host WASP-65 is a G6 star (T_eff = 5600 K, [Fe/H] = -0.07 +/- 0.07, age > 8 Gyr); WASP-75 is an F9 star (T_eff = 6100 K, [Fe/H] = 0.07 +/- 0.09, age of 3 Gyr). WASP-65b is one of the densest known exoplanets in the mass range 0.1 and 2.0 M_J (rho_pl = 1.13 +/- 0.08 rho_J), a mass range where a large fraction of planets are found to be inflated with respect to theoretical planet models. WASP-65b is one of only a handful of planets with masses of around 1.5 M_J, a mass regime surprisingly underrepresented among the currently known hot Jupiters. The radius of Jupiter-mass WASP-75b is slightly inflated (< 10%) as compared to theoretical planet models with no core, and has a density similar to that of Saturn (rho_pl = 0.52 +/- 0.06 rho_J).

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