arXiv subjects

Brett Addison

Publications and source records attributed to Brett Addison.

18 recordsLinked to original sources

arXiv2024

HD 21520 b: a warm sub-Neptune transiting a bright G dwarf

We report the discovery and validation of HD 21520 b, a transiting planet found with TESS and orbiting a bright G dwarf (V=9.2, $T_{eff} = 5871 \pm 62$ K, $R_{\star} = 1.04\pm 0.02\, R_{\odot}$). HD 21520 b was originally alerted as a system (TOI-4320) consisting of two planet candidates with periods of 703.6 and 46.4 days. However, our analysis supports instead a single-planet system with an orbital period of $25.1292\pm0.0001$ days and radius of $2.70 \pm 0.09\, R_{\oplus}$. Three full transits in sectors 4, 30 and 31 match this period and have transit depths and durations in agreement with each other, as does a partial transit in sector 3. We also observe transits using CHEOPS and LCOGT. SOAR and Gemini high-resolution imaging do not indicate the presence of any nearby companions, and MINERVA-Australis and CORALIE radial velocities rule out an on-target spectroscopic binary. Additionally, we use ESPRESSO radial velocities to obtain a tentative mass measurement of $7.9^{+3.2}_{-3.0}\, M_{\oplus}$, with a 3-$\sigma$ upper limit of 17.7 $M_{\oplus}$. Due to the bright nature of its host and likely significant gas envelope of the planet, HD 21520 b is a promising candidate for further mass measurements and for atmospheric characterization.

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arXiv2023

TOI-1994b: A Low Mass Eccentric Brown Dwarf Transiting A Subgiant Star

We present the discovery of TOI-1994b, a low-mass brown dwarf transiting a hot subgiant star on a moderately eccentric orbit. TOI-1994 has an effective temperature of $7700^{+720}_{-410}$ K, V magnitude of 10.51 mag and log(g) of $3.982^{+0.067}_{-0.065}$. The brown dwarf has a mass of $22.1^{+2.6}_{-2.5}$ $M_J$, a period of 4.034 days, an eccentricity of $0.341^{+0.054}_{-0.059}$, and a radius of $1.220^{+0.082}_{-0.071}$ $R_J$. TOI-1994b is more eccentric than other transiting brown dwarfs with similar masses and periods. The population of low mass brown dwarfs may have properties similar to planetary systems if they were formed in the same way, but the short orbital period and high eccentricity of TOI-1994b may contrast this theory. An evolved host provides a valuable opportunity to understand the influence stellar evolution has on the substellar companion's fundamental properties. With precise age, mass, and radius, the global analysis and characterization of TOI-1994b augments the small number of transiting brown dwarfs and allows the testing of substellar evolution models.

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arXiv2023

Three Saturn-mass planets transiting F-type stars revealed with TESS and HARPS

While the sample of confirmed exoplanets continues to increase, the population of transiting exoplanets around early-type stars is still limited. These planets allow us to investigate the planet properties and formation pathways over a wide range of stellar masses and study the impact of high irradiation on hot Jupiters orbiting such stars. We report the discovery of TOI-615b, TOI-622b, and TOI-2641b, three Saturn-mass planets transiting main sequence, F-type stars. The planets were identified by the Transiting Exoplanet Survey Satellite (TESS) and confirmed with complementary ground-based and radial velocity observations. TOI-615b is a highly irradiated ($\sim$1277 $F_{\oplus}$) and bloated Saturn-mass planet (1.69$^{+0.05}_{-0.06}$$R_{Jup}$ and 0.43$^{+0.09}_{-0.08}$$M_{Jup}$) in a 4.66 day orbit transiting a 6850 K star. TOI-622b has a radius of 0.82$^{+0.03}_{-0.03}$$R_{Jup}$ and a mass of 0.30$^{+0.07}_{-0.08}$~$M_{Jup}$ in a 6.40 day orbit. Despite its high insolation flux ($\sim$600 $F_{\oplus}$), TOI-622b does not show any evidence of radius inflation. TOI-2641b is a 0.39$^{+0.02}_{-0.04}$$M_{Jup}$ planet in a 4.88 day orbit with a grazing transit (b = 1.04$^{+0.05}_{-0.06 }$) that results in a poorly constrained radius of 1.61$^{+0.46}_{-0.64}$$R_{Jup}$. Additionally, TOI-615b is considered attractive for atmospheric studies via transmission spectroscopy with ground-based spectrographs and $\textit{JWST}$. Future atmospheric and spin-orbit alignment observations are essential since they can provide information on the atmospheric composition, formation and migration of exoplanets across various stellar types.

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arXiv2022

Spinning up a Daze: TESS Uncovers a Hot Jupiter orbiting the Rapid-Rotator TOI-778

NASA's Transiting Exoplanet Survey Satellite (TESS) mission, has been uncovering a growing number of exoplanets orbiting nearby, bright stars. Most exoplanets that have been discovered by TESS orbit narrow-line, slow-rotating stars, facilitating the confirmation and mass determination of these worlds. We present the discovery of a hot Jupiter orbiting a rapidly rotating ($v\sin{(i)}= 35.1\pm1.0$km/s) early F3V-dwarf, HD115447 (TOI-778). The transit signal taken from Sectors 10 and 37 of TESS's initial detection of the exoplanet is combined with follow-up ground-based photometry and velocity measurements taken from Minerva-Australis, TRES, CORALIE and CHIRON to confirm and characterise TOI-778b. A joint analysis of the light curves and the radial velocity measurements yield a mass, radius, and orbital period for TOI-778b of $2.76^{+0.24}_{-0.23}$Mjup, $1.370\pm0.043$Rjup and $\sim4.63$ days, respectively. The planet orbits a bright ($V = 9.1$mag) F3-dwarf with $M=1.40\pm0.05$Msun, $R=1.70\pm0.05$Rsun, and $\log g=4.05\pm0.17$. We observed a spectroscopic transit of TOI-778b, which allowed us to derive a sky-projected spin-orbit angle of $18^{\circ}\pm11^{\circ}$, consistent with an aligned planetary system. This discovery demonstrates the capability of smaller aperture telescopes such as Minerva-Australis to detect the radial velocity signals produced by planets orbiting broad-line, rapidly rotating stars.

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arXiv2022

A sub-Neptune transiting the young field star HD 18599 at 40 pc

Transiting exoplanets orbiting young nearby stars are ideal laboratories for testing theories of planet formation and evolution. However, to date only a handful of stars with age <1 Gyr have been found to host transiting exoplanets. Here we present the discovery and validation of a sub-Neptune around HD 18599, a young (300 Myr), nearby (d=40 pc) K star. We validate the transiting planet candidate as a bona fide planet using data from the TESS, Spitzer, and Gaia missions, ground-based photometry from IRSF, LCO, PEST, and NGTS, speckle imaging from Gemini, and spectroscopy from CHIRON, NRES, FEROS, and Minerva-Australis. The planet has an orbital period of 4.13 d, and a radius of 2.7Rearth. The RV data yields a 3-sigma mass upper limit of 30.5Mearth which is explained by either a massive companion or the large observed jitter typical for a young star. The brightness of the host star (V~9 mag) makes it conducive to detailed characterization via Doppler mass measurement which will provide a rare view into the interior structure of young planets.

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arXiv2022

A dense mini-Neptune orbiting the bright young star HD 18599

Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here we present the characterization of a new mini-Neptune planet orbiting the bright (V=9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS light curves from Sectors 2, 3, 29, and 30, with an orbital period of 4.138~days. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.5$\pm$4.6~M$_\oplus$. When we combine this with the measured radius from TESS, of 2.70$\pm$0.05~R$_\oplus$, we find a high planetary density of 7.1$\pm$1.4~g cm$^{-3}$. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23% H$_2$O and 77% Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy.

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arXiv2022

Another Shipment of Six Short-Period Giant Planets from TESS

We present the discovery and characterization of six short-period, transiting giant planets from NASA's Transiting Exoplanet Survey Satellite (TESS) -- TOI-1811 (TIC 376524552), TOI-2025 (TIC 394050135), TOI-2145 (TIC 88992642), TOI-2152 (TIC 395393265), TOI-2154 (TIC 428787891), & TOI-2497 (TIC 97568467). All six planets orbit bright host stars (8.9 <G< 11.8, 7.7 <K< 10.1). Using a combination of time-series photometric and spectroscopic follow-up observations from the TESS Follow-up Observing Program (TFOP) Working Group, we have determined that the planets are Jovian-sized (R$_{P}$ = 1.00-1.45 R$_{J}$), have masses ranging from 0.92 to 5.35 M$_{J}$, and orbit F, G, and K stars (4753 $<$ T$_{eff}$ $<$ 7360 K). We detect a significant orbital eccentricity for the three longest-period systems in our sample: TOI-2025 b (P = 8.872 days, $e$ = $0.220\pm0.053$), TOI-2145 b (P = 10.261 days, $e$ = $0.182^{+0.039}_{-0.049}$), and TOI-2497 b (P = 10.656 days, $e$ = $0.196^{+0.059}_{-0.053}$). TOI-2145 b and TOI-2497 b both orbit subgiant host stars (3.8 $<$ $\log$ g $<$4.0), but these planets show no sign of inflation despite very high levels of irradiation. The lack of inflation may be explained by the high mass of the planets; $5.35^{+0.32}_{-0.35}$ M$_{\rm J}$ (TOI-2145 b) and $5.21\pm0.52$ M$_{\rm J}$ (TOI-2497 b). These six new discoveries contribute to the larger community effort to use {\it TESS} to create a magnitude-complete, self-consistent sample of giant planets with well-determined parameters for future detailed studies.

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arXiv2022

Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No evidence for Temporal Variation of the Spin-Orbit Angle

We present 12 new transit light curves and 16 new out-of-transit radial velocity measurements for the XO-3 system. By modelling our newly collected measurements together with archival photometric and Doppler velocimetric data, we confirmed the unusual configuration of the XO-3 system, which contains a massive planet ($M_P=11.92^{+0.59}_{-0.63} M_J$) on a relatively eccentric ($e=0.2853^{+0.0027}_{-0.0026}$) and short-period ($3.19152 \pm 0.00145\,$day) orbit around a massive star ($M_*=1.219^{+0.090}_{-0.095} M_{\odot}$). Furthermore, we find no strong evidence for a temporal change of either $V\sin i_{*}$ (and by extension, the stellar spin vector of XO-3), or the transit profile (and thus orbital angular momentum vector of XO-3b). We conclude that the discrepancy in previous Rossiter-McLaughlin measurements ($70.0^{\circ} \pm 15.0^{\circ}$ (Hebrard et al. 2008); $37.3^{\circ} \pm 3.7^{\circ}$ (Winn et al. 2009); $37.3^{\circ} \pm 3.0^{\circ}$ (Hirano et al. 2011)) may have stemmed from systematic noise sources.

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arXiv2021

Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System

We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic is a young (22 Myr) early M dwarf known to host two transiting planets - $P_{b}\sim8.46$ days, $R_{b}=4.38_{-0.18}^{+0.18}\ R_{\oplus}$, $P_{c}\sim18.86$ days, $R_{c}=3.51_{-0.16}^{+0.16}\ R_{\oplus}$. With visible RVs from CARMENES-VIS, CHIRON, HARPS, HIRES, {\sc {\textsc{Minerva}}}-Australis, and TRES, as well as near-infrared (NIR) RVs from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a $5\sigma$ upper limit to the mass of AU Mic c of $M_{c}\leq20.13\ M_{\oplus}$ and present a refined mass of AU Mic b of $M_{b}=20.12_{-1.57}^{+1.72}\ M_{\oplus}$. Used in our analyses is a new RV modeling toolkit to exploit the wavelength dependence of stellar activity present in our RVs via wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible and near-infrared RVs, we also compute the temporal evolution of RV-``color'' and introduce a regressional method to aid in isolating Keplerian from stellar activity signals when modeling RVs in future works. Using a multi-wavelength Gaussian process model, we demonstrate the ability to recover injected planets at $5\sigma$ significance with semi-amplitudes down to $\approx$ 10\,m\,s$^{-1}$ with a known ephemeris, more than an order of magnitude below the stellar activity amplitude. However, we find that the accuracy of the recovered semi-amplitudes is $\sim$50\% for such signals with our model.

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arXiv2021

A transiting warm giant planet around the young active star TOI-201

We present the confirmation of the eccentric warm giant planet TOI-201 b, first identified as a candidate in \textit{TESS} photometry (Sectors 1-8, 10-13, and 27-28) and confirmed using ground-based photometry from NGTS and radial velocities from FEROS, HARPS, CORALIE, and \textsc{Minerva}-Australis. TOI-201 b orbits a young ($\mathrm{0.87^{+0.46}_{-0.49} \, Gyr}$) and bright(V=9.07 mag) F-type star with a $\mathrm{52.9781 \, d}$ period. The planet has a mass of $\mathrm{0.42^{+0.05}_{-0.03}\, M_J}$, a radius of $\mathrm{1.008^{+0.012}_{-0.015}\, R_J}$, and an orbital eccentricity of $0.28^{+0.06}_{-0.09}$; it appears to still be undergoing fairly rapid cooling, as expected given the youth of the host star. The star also shows long-term variability in both the radial velocities and several activity indicators, which we attribute to stellar activity. The discovery and characterization of warm giant planets such as TOI-201 b is important for constraining formation and evolution theories for giant planets.

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arXiv2021

TESS Delivers Five New Hot Giant Planets Orbiting Bright Stars from the Full Frame Images

We present the discovery and characterization of five hot and warm Jupiters -- TOI-628 b (TIC 281408474; HD 288842), TOI-640 b (TIC 147977348), TOI-1333 b (TIC 395171208, BD+47 3521A), TOI-1478 b (TIC 409794137), and TOI-1601 b (TIC 139375960) -- based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The five planets were identified from the full frame images and were confirmed through a series of photometric and spectroscopic follow-up observations by the $TESS$ Follow-up Observing Program (TFOP) Working Group. The planets are all Jovian size (R$_{\rm P}$ = 1.01-1.77 R$_{\rm J}$) and have masses that range from 0.85 to 6.33 M$_{\rm J}$. The host stars of these systems have F and G spectral types (5595 $\le$ T$_{\rm eff}$ $\le$ 6460 K) and are all relatively bright (9 $ 1.7R$_{\rm J}$, possibly a result of its host star's evolution) and resides on an orbit with a period longer than 5 days. TOI-628 b is the most massive hot Jupiter discovered to date by $TESS$ with a measured mass of $6.31^{+0.28}_{-0.30}$ M$_{\rm J}$ and a statistically significant, non-zero orbital eccentricity of e = $0.074^{+0.021}_{-0.022}$. This planet would not have had enough time to circularize through tidal forces from our analysis, suggesting that it might be remnant eccentricity from its migration. The longest period planet in this sample, TOI-1478 b (P = 10.18 days), is a warm Jupiter in a circular orbit around a near-Solar analogue. NASA's $TESS$ mission is continuing to increase the sample of well-characterized hot and warm Jupiters, complementing its primary mission goals.

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arXiv2019

TOI-677 b: A Warm Jupiter (P=11.2d) on an eccentric orbit transiting a late F-type star

We report the discovery of TOI-677 b, first identified as a candidate in light curves obtained within Sectors 9 and 10 of the Transiting Exoplanet Survey Satellite (TESS) mission and confirmed with radial velocities. TOI-677 b has a mass of M_p = 1.236$^{+0.069}_{-0.067}$ M_J, a radius of R_p = 1.170 +- 0.03 R_J,and orbits its bright host star (V=9.8 mag) with an orbital period of 11.23660 +- 0.00011 d, on an eccentric orbit with e = 0.435 +- 0.024. The host star has a mass of M_* = 1.181 +- 0.058 M_sun, a radius of R_* = 1.28 +- 0.03 R_sun, an age of 2.92$^{+0.80}_{-0.73}$ Gyr and solar metallicity, properties consistent with a main sequence late F star with T_eff = 6295 +- 77 K. We find evidence in the radial velocity measurements of a secondary long term signal which could be due to an outer companion. The TOI-677 b system is a well suited target for Rossiter-Mclaughlin observations that can constrain migration mechanisms of close-in giant planets.

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arXiv2019

TOI-222: a single-transit TESS candidate revealed to be a 34-day eclipsing binary with CORALIE, EulerCam and NGTS

We report the period, eccentricity, and mass determination for the TESS single-transit event candidate TOI-222, which displayed a single 3000 ppm transit in the TESS two-minute cadence data from Sector 2. We determine the orbital period via radial velocity measurements (P=33.9,days), which allowed for ground-based photometric detection of two subsequent transits. Our data show that the companion to TOI-222 is a low mass star, with a radius of $0.18_{-0.10}^{+0.39}$ Rsun and a mass of $0.23\pm0.01$ Msun. This discovery showcases the ability to efficiently discover long-period systems from TESS single transit events using a combination of radial velocity monitoring coupled with high precision ground-based photometry.

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arXiv2019

TESS Spots a Compact System of Super-Earths around the Naked-Eye Star HR 858

Transiting Exoplanet Survey Satellite (TESS) observations have revealed a compact multi-planet system around the sixth-magnitude star HR 858 (TIC 178155732, TOI 396), located 32 parsecs away. Three planets, each about twice the size of Earth, transit this slightly-evolved, late F-type star, which is also a member of a visual binary. Two of the planets may be in mean motion resonance. We analyze the TESS observations, using novel methods to model and remove instrumental systematic errors, and combine these data with follow-up observations taken from a suite of ground-based telescopes to characterize the planetary system. The HR 858 planets are enticing targets for precise radial velocity observations, secondary eclipse spectroscopy, and measurements of the Rossiter-McLaughlin effect.

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arXiv2019

Minerva-Australis I: Design, Commissioning, & First Photometric Results

The Minerva-Australis telescope array is a facility dedicated to the follow-up, confirmation, characterisation, and mass measurement of bright transiting planets discovered by the Transiting Exoplanet Survey Satellite (TESS) -- a category in which it is almost unique in the southern hemisphere. It is located at the University of Southern Queensland's Mount Kent Observatory near Toowoomba, Australia. Its flexible design enables multiple 0.7m robotic telescopes to be used both in combination, and independently, for high-resolution spectroscopy and precision photometry of TESS transit planet candidates. Minerva-Australis also enables complementary studies of exoplanet spin-orbit alignments via Doppler observations of the Rossiter-McLaughlin effect, radial velocity searches for non-transiting planets, planet searches using transit timing variations, and ephemeris refinement for TESS planets. In this first paper, we describe the design, photometric instrumentation, software, and science goals of Minerva-Australis, and note key differences from its Northern hemisphere counterpart -- the Minerva array. We use recent transit observations of four planets--WASP-2b, WASP-44b, WASP-45b, and HD 189733b to demonstrate the photometric capabilities of Minerva-Australis.

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arXiv2018

HD 202772A B: A Transiting Hot Jupiter Around A Bright, Mildly Evolved Star In A Visual Binary Discovered By Tess

We report the first confirmation of a hot Jupiter discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HD 202772A b. The transit signal was detected in the data from TESS Sector 1, and was confirmed to be of planetary origin through radial-velocity measurements. HD 202772A b is orbiting a mildly evolved star with a period of 3.3 days. With an apparent magnitude of V = 8.3, the star is among the brightest known to host a hot Jupiter. Based on the 27days of TESS photometry, and radial velocity data from the CHIRON and HARPS spectrographs, the planet has a mass of 1.008+/-0.074 M_J and radius of 1.562+/-0.053 R_J , making it an inflated gas giant. HD 202772A b is a rare example of a transiting hot Jupiter around a quickly evolving star. It is also one of the most strongly irradiated hot Jupiters currently known.

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arXiv2017

Stellar Spin-Orbit Alignment for Kepler-9, a Multi-transiting Planetary system with Two Outer Planets Near 2:1 Resonance

We present spectroscopic measurements of the Rossiter-McLaughlin effect for the planet b of Kepler-9 multi-transiting planet system. The resulting sky-projected spin-orbit angle is $\lambda=-13^{\circ} \pm 16^{\circ}$, which favors an aligned system and strongly disfavors highly misaligned, polar, and retrograde orbits. Including Kepler-9, there are now a total of 4 Rossiter-McLaughlin effect measurements for multiplanet systems, all of which are consistent with spin-orbit alignment.

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arXiv2008

Thermal AGN Signatures in Blazars

Long ignored in blazars because of the dominance of the beamed radiation from the jet, the topic of thermal emissions in these objects is just beginning to be explored. While this emission is weak in most blazars compared to the dominant nonthermal jet components, there is a growing body of evidence that suggests that thermal emission is observable even in the most highly beamed objects. The emitting regions, which can include the accretion disk as well as the torus, are key parts of the central engine which also powers the jets. They also may be of critical importance in helping us decide between unified scheme models. We will review the observational evidence for thermal emissions in blazars, with an emphasis on recent work, and the spectral and variability characteristics that have been observed. The majority of the evidence for thermal emission in blazars (now observed in several objects) has come as a result of multiwavelength campaigns, where the object showed a clear bump in the optical-UV in a faint state. However, evidence exists from other avenues as well, including both purely spectral and variability based arguments as well as statistical analyses of large samples of objects. We will also discuss the impact of thermal emission on an object's overall SED, including its Comptonized signatures. Finally, we will assess the current standing of unified scheme models as respects thermal signatures and the prospects for detecting thermal emission with new telescopes and missions, and further utilizing it as a probe of the central engine of blazars.

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