Abstract
AU Mic is a young (∼24 Myr), pre-main-sequence M dwarf star that was observed in the first month of science observations of the Transiting Exoplanet Survey Satellite (TESS) and reobserved 2 ...years later. This target has photometric variability from a variety of sources that is readily apparent in the TESS light curves; spots induce modulation in the light curve, flares are present throughout (manifesting as sharp rises with slow exponential decay phases), and transits of AU Mic b may be seen by eye as dips in the light curve. We present a combined analysis of both TESS Sector 1 and Sector 27 AU Mic light curves including the new 20 s cadence data from TESS Year 3. We compare flare rates between both observations and analyze the spot evolution, showing that the activity levels increase slightly from Sector 1 to Sector 27. Furthermore, the 20 s data collection allows us to detect more flares, smaller flares, and better resolve flare morphology in white light as compared to the 2 minute data collection mode. We also refine the parameters for AU Mic b by fitting three additional transits of AU Mic b from Sector 27 using a model that includes stellar activity. We show that the transits exhibit clear transit timing variations with an amplitude of ∼80 s. We also detect three transits of a 2.8
R
⊕
planet, AU Mic c, which has a period of 18.86 days.
Given the frequency of stellar multiplicity in the solar neighborhood, it is important to study the impacts this can have on exoplanet properties and orbital dynamics. There have been numerous ...imaging survey projects established to detect possible low-mass stellar companions to exoplanet host stars. Here, we provide the results from a systematic speckle imaging survey of known exoplanet host stars. In total, 71 stars were observed at 692 and 880 nm bands using the Differential Speckle Survey Instrument at the Gemini-north Observatory. Our results show that all but two of the stars included in this sample have no evidence of stellar companions with luminosities down to the detection and projected separation limits of our instrumentation. The mass-luminosity relationship is used to estimate the maximum mass a stellar companion can have without being detected. These results are used to discuss the potential for further radial velocity follow-up and interpretation of companion signals.
We explore the transit timing variations (TTVs) of the young (22 Myr) nearby AU Mic planetary system. For AU
Mic b, we introduce three Spitzer (4.5 μm) transits, five TESS transits, 11 LCO transits, ...one PEST transit, one
Brierfield transit, and two transit timing measurements from Rossiter–McLaughlin observations; for AU Mic c, we
introduce three TESS transits. We present two independent TTV analyses. First, we use EXOFASTv2 to jointly
model the Spitzer and ground-based transits and obtain the midpoint transit times. We then construct an O − C
diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent
photodynamical analysis. We recover a TTV mass for AU Mic c of -10.8+2.22.3 M⊕. We compare the TTV-derived
constraints to a recent radial velocity (RV) mass determination. We also observe excess TTVs that do not appear to
be consistent with the dynamical interactions of b and c alone or due to spots or flares. Thus, we present a
hypothetical nontransiting “middle-d” candidate exoplanet that is consistent with the observed TTVs and candidate
RV signal and would establish the AU Mic system as a compact resonant multiplanet chain in a 4:6:9 period
commensurability. These results demonstrate that the AU Mic planetary system is dynamically interacting,
producing detectable TTVs, and the implied orbital dynamics may inform the formation mechanisms for this
young system. We recommend future RV and TTV observations of AU Mic b and c to further constrain the masses
and confirm the existence of possible additional planet(s).
ABSTRACT An important aspect of searching for exoplanets is understanding the binarity of the host stars. It is particularly important, because nearly half of the solar-like stars within our own ...Milky Way are part of binary or multiple systems. Moreover, the presence of two or more stars within a system can place further constraints on planetary formation, evolution, and orbital dynamics. As part of our survey of almost a hundred host stars, we obtained images at 692 and 880 nm bands using the Differential Speckle Survey Instrument (DSSI) at the Gemini-North Observatory. From our survey, we detect stellar companions to HD 2638 and HD 164509. The stellar companion to HD 2638 has been previously detected, but the companion to HD 164509 is a newly discovered companion. The angular separation for HD 2638 is 0.512 0 002 and for HD 164509 is . This corresponds to a projected separation of 25.6 1.9 au and 36.5 1.9 au, respectively. By employing stellar isochrone models, we estimate the mass of the stellar companions of HD 2638 and HD 164509 to be 0.483 0.007 M and , respectively, and their effective temperatures to be 3570 8 K and 3450 7 K, respectively. These results are consistent with the detected companions being late-type M dwarfs.
Exoplanetary sciences is a relatively new field of study that has grown beyond just detection method to include, among other things, planetary and atmospheric characterizations. Recent missions such ...as Kepler, K2, and TESS has resulted in more than 5 000 planets being validated or confirmed, allowing us to delve deeply into studying the properties of these planets and their host systems. In this thesis, I present the Transit Timing Variations (TTVs) of AU Mic b and c and the validation of the candidate planet AU Mic d. AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess TTVs that cannot be accounted for by the two known transiting planets b and c nor stellar activity. 37 transit observations (including one ASTEP, one Brierfield, 23 LCOGT, one PEST, three Spitzer, and eight TESS), three Rossiter-McLaughlin (R-M) observations (ESPRESSO, iSHELL, and SPIRou), and nine CHEOPS transit midpoint times are included in our TTV analyses. First, we use EXOFASTv2 to jointly model the transit light curves to obtain the transit midpoint times. We then construct an O–C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8+2.3−2.2 M⊕. We compare the TTV-derived constraints to a recent radial-velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone, and do not appear to be due to spots or flares; therefore, we hypothesize the existence of a third planet AU Mic d that is driving the observed excess TTVs. I calculate d’s potential orbital periods by modeling the observed super-period in AU Mic b’s TTVs. Next, we explore several possible configurations for planet d, including having d be interior to b and having d be between b and c. We generate TTV log-likelihood periodograms to explore possible solutions for the orbital period of planet d and then follow those up with detailed TTV and RV MCMC modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, AU Mic b’s TTV super-period, stability tests, and Occam’s razor arguments regarding near-mean motion orbital resonance (MMR) chains and coplanarity of AU Mic system, the most-favored orbital period of AU Mic d is 12.73812 ± 0.00128 days (TC,d = 2458333.32110 ± 0.35836 BJD), which puts the three planets near a 4:6:9 MMR. The mass for d from the most plausible case is Md = 1.013 ± 0.146 M⊕, making this planet Earth-like in mass. This would make AU Mic the first known young star to host an Earth-mass planet. Lastly, I characterize AU Mic b’s atmosphere with Transit Depth Variations and found the effective radius of AU Mic b to be significantly smaller at 4.5 μm than at optical range, a phenomenon that is similarly seen in another young planet K2-33 b. The mass-radius analysis of AU Mic b indicates that it is comparable to that of a 10% H + He planet; however, since it’s atmosphere is known to be evaporating, AU Mic b is evolving into a smaller and denser planet over the next several Myrs or Gyrs. The presence of near-MMRs in a very young system implies that compact planetary systems can develop resonant chains very early on, which can quickly establish the stability of the systems. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c. If AU Mic d does transit, it will serve as an incredibly valuable case study for characterizing the atmosphere of young terrestrial planets and understanding its evolution.
Abstract
The Kepler and TESS missions have demonstrated that planets are ubiquitous. However, the success of these missions heavily depends on ground-based radial velocity (RV) surveys, which ...combined with transit photometry can yield bulk densities and orbital properties. While most Kepler host stars are too faint for detailed follow-up observations, TESS is detecting planets orbiting nearby bright stars that are more amenable to RV characterization. Here, we introduce the TESS-Keck Survey (TKS), an RV program using ∼100 nights on Keck/HIRES to study exoplanets identified by TESS. The primary survey aims are investigating the link between stellar properties and the compositions of small planets; studying how the diversity of system architectures depends on dynamical configurations or planet multiplicity; identifying prime candidates for atmospheric studies with JWST; and understanding the role of stellar evolution in shaping planetary systems. We present a fully automated target selection algorithm, which yielded 103 planets in 86 systems for the final TKS sample. Most TKS hosts are inactive, solar-like, main-sequence stars (4500 K ≤
T
eff
<6000 K) at a wide range of metallicities. The selected TKS sample contains 71 small planets (
R
p
≤ 4
R
⊕
), 11 systems with multiple transiting candidates, six sub-day-period planets and three planets that are in or near the habitable zone (
S
inc
≤ 10
S
⊕
) of their host star. The target selection described here will facilitate the comparison of measured planet masses, densities, and eccentricities to predictions from planet population models. Our target selection software is publicly available and can be adapted for any survey that requires a balance of multiple science interests within a given telescope allocation.
ABSTRACT
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), and 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 Working Group, we have determined that the planets are Jovian-sized (RP = 0.99--1.45 RJ), have masses ranging from 0.92 to 5.26 MJ, and orbit F, G, and K stars (4766 ≤ Teff ≤ 7360 K). We detect a significant orbital eccentricity for the three longest-period systems in our sample: TOI-2025 b (P = 8.872 d, 0.394$^{+0.035}_{-0.038}$), TOI-2145 b (P = 10.261 d, e = $0.208^{+0.034}_{-0.047}$), and TOI-2497 b (P = 10.656 d, e = $0.195^{+0.043}_{-0.040}$). 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; $5.26^{+0.38}_{-0.37}$ MJ (TOI-2145 b) and 4.82 ± 0.41 MJ (TOI-2497 b). These six new discoveries contribute to the larger community effort to use TESS to create a magnitude-complete, self-consistent sample of giant planets with well-determined parameters for future detailed studies.
Abstract
Multiplanet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf (
V
= 11.6,
...K
= 9.9) and four transiting sub-Neptunes identified by TESS with orbital periods of 4.31, 5.90, 18.66, and 37.92 days. We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii (2.97 ± 0.06
R
⊕
, 2.47 ± 0.08
R
⊕
, 3.46 ± 0.09
R
⊕
, and 3.72 ± 0.16
R
⊕
) and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets (8.1 ± 1.1
M
⊕
, 8.8 ± 1.2
M
⊕
, 5.3 ± 1.7
M
⊕
, and 14.8 ± 2.3
M
⊕
). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance (
P
e
/
P
d
= 2.03) and exhibit transit-timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only five systems with measured masses and radii for all four transiting planets. The planet densities range from 0.70 ± 0.24 to 3.21 ± 0.44 g cm
−3
, implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 ± 3.6
M
⊕
. This planet candidate is exterior to TOI-1246 e, with a candidate period of 93.8 days, and we discuss the implications if it is confirmed to be planetary in nature.
Abstract
AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar ...activity. We present the statistical “validation” of the tentative planet AU Mic d (even though there are examples of “confirmed” planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using
EXOFASTv2
and extract the transit midpoint times. Next, we construct an
O
−
C
diagram and use
Exo-Striker
to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for d’s period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days (
T
C
,d
= 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511
M
⊕
, making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planet’s atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c.
THREE TEMPERATE NEPTUNES ORBITING NEARBY STARS Fulton, Benjamin J.; Howard, Andrew W.; Weiss, Lauren M. ...
The Astrophysical journal,
10/2016, Letnik:
830, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We present the discovery of three modestly irradiated, roughly Neptune-mass planets orbiting three nearby Solar-type stars. HD 42618 b has a minimum mass of 15.4 ± 2.4
, a semimajor axis of ...0.55 au, an equilibrium temperature of 337 K, and is the first planet discovered to orbit the solar analogue host star, HD 42618. We also discover new planets orbiting the known exoplanet host stars HD 164922 and HD 143761 (
ρ
CrB). The new planet orbiting HD 164922 has a minimum mass of 12.9 ± 1.6
and orbits interior to the previously known Jovian mass planet orbiting at 2.1 au. HD 164922 c has a semimajor axis of 0.34 au and an equilibrium temperature of 418 K. HD 143761 c orbits with a semimajor axis of 0.44 au, has a minimum mass of 25 ± 2
, and is the warmest of the three new planets with an equilibrium temperature of 445 K. It orbits exterior to the previously known warm Jupiter in the system. A transit search using space-based CoRoT data and ground-based photometry from the Automated Photometric Telescopes (APTs) at Fairborn Observatory failed to detect any transits, but the precise, high-cadence APT photometry helped to disentangle planetary-reflex motion from stellar activity. These planets were discovered as part of an ongoing radial velocity survey of bright, nearby, chromospherically inactive stars using the Automated Planet Finder (APF) telescope at Lick Observatory. The high-cadence APF data combined with nearly two decades of radial velocity data from Keck Observatory and gives unprecedented sensitivity to both short-period low-mass, and long-period intermediate-mass planets.
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