Tianjun Gan

Tsinghua University

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Karen A. Collins

Center for Astrophysics Harvard & Smithsonian

Jon M. Jenkins

Ames Research Center

G. Ricker

Massachusetts Institute of Technology

David W. Latham

Center for Astrophysics Harvard & Smithsonian

Sara Seager

Massachusetts Institute of Technology

Joshua N. Winn

Princeton University

R. Vanderspek

Massachusetts Institute of Technology

Avi Shporer

Massachusetts Institute of Technology

Kevin I. Collins

George Mason University

Steve B. Howell

Ames Research Center

Cooperative Institutions

Max Planck Institute for Astronomy

143

Max Planck Society

125

Massachusetts Institute of Technology

123

Centre National de la Recherche Scientifique

110

Center for Astrophysics Harvard & Smithsonian

108

California Institute of Technology

Goddard Space Flight Center

Instituto de Astrofísica de Canarias

University of Geneva

Chinese Academy of Sciences

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Discovery of a hot, transiting, Earth-sized planet and a second temperate, non-transiting planet around the M4 dwarf GJ 3473 (TOI-488)

Astronomy and Astrophysics (2020)

J. Kemmer S. Stock D. Kossakowski A. Kaminski Karan Molaverdikhani

We present the confirmation and characterisation of GJ 3473 b (G 50--16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal ($P=1.1980035\pm0.0000018\mathrm{\,d}$) was first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass, $M_b = 1.86\pm0.30\,\mathrm{M_\oplus},$ and radius, $R_b = {1.264\pm0.050}\,\mathrm{R_\oplus}$. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass, $M_c \sin{i} = {7.41\pm0.91}\,\mathrm{M_\oplus,}$ and orbital period, $P_c={15.509\pm0.033}\,\mathrm{d}$. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy.

Super-Earth

Radial velocity

Star (game theory)

10.1051/0004-6361/202038967

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Citations (34)

Characterization of a set of small planets with TESS and CHEOPS and an analysis of photometric performance

arXiv (Cornell University) (2023)

Dominic Oddo Diana Dragomir A. Brandeker H. P. Osborn Karen A. Collins

The radius valley carries implications for how the atmospheres of small planets form and evolve, but this feature is visible only with highly precise characterizations of many small planets. We present the characterization of nine planets and one planet candidate with both NASA TESS and ESA CHEOPS observations, which adds to the overall population of planets bordering the radius valley. While four of our planets - TOI 118 b, TOI 455 b, TOI 560 b, and TOI 562 b - have already been published, we vet and validate transit signals as planetary using follow-up observations for five new TESS planets, including TOI 198 b, TOI 244 b, TOI 262 b, TOI 444 b, and TOI 470 b. While a three times increase in primary mirror size should mean that one CHEOPS transit yields an equivalent model uncertainty in transit depth as about nine TESS transits in the case that the star is equally as bright in both bands, we find that our CHEOPS transits typically yield uncertainties equivalent to between two and 12 TESS transits, averaging 5.9 equivalent transits. Therefore, we find that while our fits to CHEOPS transits provide overall lower uncertainties on transit depth and better precision relative to fits to TESS transits, our uncertainties for these fits do not always match expected predictions given photon-limited noise. We find no correlations between number of equivalent transits and any physical parameters, indicating that this behavior is not strictly systematic, but rather might be due to other factors such as in-transit gaps during CHEOPS visits or nonhomogeneous detrending of CHEOPS light curves.

10.48550/arxiv.2301.08162

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VizieR Online Data Catalog: Differential photometry & RVs of HAT-P-69 & HAT-P-70 (Zhou+, 2019)

yCat (2019)

George Zhou Chelsea X. Huang G. Á. Bakos J. D. Hartman David W. Latham

Source

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The TESS Grand Unified Hot Jupiter Survey. I. Ten TESS Planets

The Astronomical Journal (2022)

Samuel W. Yee Joshua N. Winn J. D. Hartman Joseph E. Rodriguez George Zhou

Abstract Hot Jupiters—short-period giant planets—were the first extrasolar planets to be discovered, but many questions about their origin remain. NASA’s Transiting Exoplanet Survey Satellite (TESS), an all-sky search for transiting planets, presents an opportunity to address these questions by constructing a uniform sample of hot Jupiters for demographic study through new detections and unifying the work of previous ground-based transit surveys. As the first results of an effort to build this large sample of planets, we report here the discovery of 10 new hot Jupiters (TOI-2193A b, TOI-2207b, TOI-2236b, TOI-2421b, TOI-2567b, TOI-2570b, TOI-3331b, TOI-3540A b, TOI-3693b, TOI-4137b). All of the planets were identified as planet candidates based on periodic flux dips observed by TESS, and were subsequently confirmed using ground-based time-series photometry, high-angular-resolution imaging, and high-resolution spectroscopy coordinated with the TESS Follow-up Observing Program. The 10 newly discovered planets orbit relatively bright F and G stars ( G < 12.5, T eff between 4800 and 6200 K). The planets’ orbital periods range from 2 to 10 days, and their masses range from 0.2 to 2.2 Jupiter masses. TOI-2421b is notable for being a Saturn-mass planet and TOI-2567b for being a “sub-Saturn,” with masses of 0.322 ± 0.073 and 0.195 ± 0.030 Jupiter masses, respectively. We also measured a detectably eccentric orbit ( e = 0.17 ± 0.05) for TOI-2207b, a planet on an 8 day orbit, while placing an upper limit of e < 0.052 for TOI-3693b, which has a 9 day orbital period. The 10 planets described here represent an important step toward using TESS to create a large and statistically useful sample of hot Jupiters.

Orbital period

Gas giant

10.3847/1538-3881/ac73ff

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Citations (15)

Publisher Correction: A super-Earth and two sub-Neptunes transiting the nearby and quiet M dwarf TOI-270

Nature Astronomy (2019)

Maximilian N. Günther F. J. Pozuelos Jason Dittmann Diana Dragomir Stephen R. Kane

QUIET

10.1038/s41550-019-0889-6

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Citations (1)

HD 183579b: a warm sub-Neptune transiting a solar twin detected by TESS

Monthly Notices of the Royal Astronomical Society (2021)

Tianjun Gan Megan Bedell Sharon X. Wang Daniel Foreman-Mackey J. Meléndez

We report the discovery and characterization of a transiting warm sub-Neptune planet around the nearby bright ($V=8.75$ mag, $K=7.15$ mag) solar twin HD 183579, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located $56.8\pm0.1$ pc away with a radius of $R_{\ast}=0.97\pm0.02\ R_{\odot}$ and a mass of $M_{\ast}=1.03\pm0.05\ M_{\odot}$. We confirm the planetary nature by combining space and ground-based photometry, spectroscopy, and imaging. We find that HD 183579b (TOI-1055b) has a radius of $R_{p}=3.53\pm0.13\ R_{\oplus}$ on a $17.47$ day orbit with a mass of $M_{p}=11.2\pm5.4\ M_{\oplus}$ ($3\sigma$ mass upper limit of $27.4\ M_{\oplus}$). HD 183579b is the fifth brightest known sub-Neptune planet system in the sky, making it an excellent target for future studies of the interior structure and atmospheric properties. By performing a line-by-line differential analysis using the high resolution and signal-to-noise ratio HARPS spectra, we find that HD 183579 joins the typical solar twin sample, without a statistically significant refractory element depletion.

Neptune

Solar mass

10.1093/mnras/stab2224

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Citations (5)

TOI-1842b: A Transiting Warm Saturn Undergoing Reinflation around an Evolving Subgiant

The Astronomical Journal (2022)

Robert A. Wittenmyer Jake T. Clark T. Trifonov Brett C. Addison D. J. Wright

Abstract The imminent launch of space telescopes designed to probe the atmospheres of exoplanets has prompted new efforts to prioritize the thousands of transiting planet candidates for follow-up characterization. We report the detection and confirmation of TOI-1842b, a warm Saturn identified by TESS and confirmed with ground-based observations from M inerva -Australis, NRES, and the Las Cumbres Observatory Global Telescope. This planet has a radius of 1.04 − 0.05 + 0.06 R J , a mass of 0.214 − 0.038 + 0.040 M J , an orbital period of 9.5739 − 0.0001 + 0.0002 days, and an extremely low density ( ρ = 0.252 ± 0.091 g cm −3 ). TOI-1842b has among the best known combinations of large atmospheric scale height (893 km) and host-star brightness ( J = 8.747 mag), making it an attractive target for atmospheric characterization. As the host star is beginning to evolve off the main sequence, TOI-1842b presents an excellent opportunity to test models of gas giant reinflation. The primary transit duration of only 4.3 hr also makes TOI-1842b an easily-schedulable target for further ground-based atmospheric characterization.

Subgiant

Orbital period

10.3847/1538-3881/ac3f39

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Citations (10)

Three low-mass companions around aged stars discovered by TESS

Monthly Notices of the Royal Astronomical Society (2023)

Zitao Lin Tianjun Gan Sharon X. Wang Avi Shporer M. Rabus

We report the discovery of three transiting low-mass companions to aged stars: a brown dwarf (TOI-2336b) and two objects near the hydrogen burning mass limit (TOI-1608b and TOI-2521b). These three systems were first identified using data from the Transiting Exoplanet Survey Satellite (TESS). TOI-2336b has a radius of $1.05\pm 0.04\ R_J$, a mass of $69.9\pm 2.3\ M_J$ and an orbital period of 7.71 days. TOI-1608b has a radius of $1.21\pm 0.06\ R_J$, a mass of $90.7\pm 3.7\ M_J$ and an orbital period of 2.47 days. TOI-2521b has a radius of $1.01\pm 0.04\ R_J$, a mass of $77.5\pm 3.3\ M_J$ and an orbital period of 5.56 days. We found all these low-mass companions are inflated. We fitted a relation between radius, mass and incident flux using the sample of known transiting brown dwarfs and low-mass M dwarfs. We found a positive correlation between the flux and the radius for brown dwarfs and for low-mass stars that is weaker than the correlation observed for giant planets. We also found that TOI-1608 and TOI-2521 are very likely to be spin-orbit synchronized, leading to the unusually rapid rotation of the primary stars considering their evolutionary stages. Our estimates indicate that both systems have much shorter spin-orbit synchronization timescales compared to their ages. These systems provide valuable insights into the evolution of stellar systems with brown dwarf and low-mass stellar companions influenced by tidal effects.

Orbital period

Low Mass

Orbit (dynamics)

10.1093/mnras/stad1745

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Citations (5)

Erratum: “TOI-2076 and TOI-1807: Two Young, Comoving Planetary Systems within 50 pc Identified by TESS that are Ideal Candidates for Further Follow Up” (2021, AJ, 162, 54)

The Astronomical Journal (2022)

Christina Hedges Alex Hughes George Zhou Trevor J. David Juliette Becker

10.3847/1538-3881/ac4477

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Citations (1)

TOI-332 b: a super dense Neptune found deep within the Neptunian desert

arXiv (Cornell University) (2023)

Ares Osborn D. J. Armstrong Jorge Fernández Fernández Henrik Knierim V. Adibekyan

To date, thousands of planets have been discovered, but there are regions of the orbital parameter space that are still bare. An example is the short period and intermediate mass/radius space known as the Neptunian desert, where planets should be easy to find but discoveries remain few. This suggests unusual formation and evolution processes are responsible for the planets residing here. We present the discovery of TOI-332 b, a planet with an ultra-short period of $0.78$ d that sits firmly within the desert. It orbits a K0 dwarf with an effective temperature of $5251 \pm 71$ K. TOI-332 b has a radius of $3.20^{+0.16}_{-0.12}$ R$_{\oplus}$, smaller than that of Neptune, but an unusually large mass of $57.2 \pm 1.6$ M$_{\oplus}$. It has one of the highest densities of any Neptune-sized planet discovered thus far at $9.6^{+1.1}_{-1.3}$ gcm$^{-3}$. A 4-layer internal structure model indicates it likely has a negligible hydrogen-helium envelope, something only found for a small handful of planets this massive, and so TOI-332 b presents an interesting challenge to planetary formation theories. We find that photoevaporation cannot account for the mass loss required to strip this planet of the Jupiter-like envelope it would have been expected to accrete. We need to look towards other scenarios, such as high-eccentricity migration, giant impacts, or gap opening in the protoplanetary disc, to try and explain this unusual discovery.

Neptune

Photoevaporation

Jupiter (rocket family)

Jupiter mass

10.48550/arxiv.2308.12137

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