CVSO 30 / PTFO 8-8695

The PTF Orion Project: a Possible Planet Transiting a T-Tauri Star
http://arxiv.org/abs/1206.1510

Quote :

We report observations of a possible young transiting planet orbiting a previously known weak-lined T-Tauri star in the 7-10Myr-old Orion-OB1a/25-Ori region. The candidate was found as part of the Palomar Transient Factory (PTF) Orion project. It has a photometric transit period of 0.448413 \pm 0.000040 days, and appears in both 2009 and 2010 PTF data. Follow-up low-precision radial velocity observations and adaptive-optics imaging suggest that the star is not an eclipsing binary, and that it is unlikely that a background source is blended with the target and mimicking the observed transit. Radial-velocity observations with the Hobby-Eberly and Keck telescopes yield a radial velocity that has the same period as the photometric event, but is offset in phase from the transit center by \approx -0.22 periods. The amplitude (half range) of the radial velocity variations is 2.4 km/s and is comparable with the expected radial velocity amplitude that stellar spots could induce. The radial velocity curve is likely dominated by stellar spot modulation and provides an upper limit to the projected companion mass of Mp sin iorb \leq 4.8\pm1.2 MJup; when combined with the orbital inclination, iorb, of the candidate planet from modeling of the transit lightcurve, we find an upper limit on the mass of the planetary candidate of Mp \leq 5.5\pm1.4 MJup. This limit implies that the planet is orbiting close to, if not inside, its Roche limiting orbital radius, so that it may be undergoing active mass loss and evaporating.

Measurement of Spin-Orbit Misalignment and Nodal Precession for the Planet around Pre-Main-Sequence Star PTFO 8-8695 From Gravity Darkening
http://arxiv.org/abs/1308.0629

Quote :

PTFO 8-8695b represents the first transiting exoplanet candidate orbiting a pre-main-sequence star. We find that the unusual lightcurve shapes of PTFO 8-8695 can be explained by transits of a planet across an oblate, gravity-darkened stellar disk. We simultaneously and self-consistently fit two separate lightcurves observed in 2009 December and 2010 December. Our two self-consistent fits yield M_p = 3.0 M_Jup and M_p = 3.6 M_Jup for assumed stellar masses of M_* = 0.34 M_Sun and M_* = 0.44 M_Sun respectively. The two fits have precession periods of 293 days and 581 days. These mass determinations (consistent with previous upper limits) along with the strength of the gravity-darkened precessing model together validate PTFO 8-8695b as just the second Hot Jupiter known to orbit an M-dwarf. Our fits show a high degree of spin-orbit misalignment in the PTFO 8-8695 system: 69 +/- 2 or 73.1 +/- 0.5 degrees, in the two cases. The large misalignment is consistent with the hypothesis that planets become Hot Jupiters with random orbital plane alignments early in a system's lifetime. We predict that as a result of the highly misaligned, precessing system, the transits should disappear for months at a time over the course of the system's precession period. The precessing, gravity-darkened model also predicts other observable effects: changing orbit inclination that could be detected by radial velocity observations, changing stellar inclination that would manifest as varying v sin i, changing projected spin-orbit alignment that could be seen by the Rossiter-McLaughlin effect, changing transit shapes over the course of the precession, and differing lightcurves as a function of wavelength. Our measured planet radii of 1.64 R_Jup and 1.68 R_Jup in each case are consistent with a young, hydrogen-dominated planet that results from a hot-start formation mechanism.

One word: wow!

If confirmed, that's a pretty incredible system: stellar oblateness is about 0.1 -- I think this makes it the most oblate known planet-hosting star, planet itself is close to its Roche limit (orbit less than 11 hours!). Lots of prospects for follow-up on the various observational effects of the precessing system.

Seems that whatever process ends up producing hot Jupiters, it can happen pretty rapidly.

Also this thread

Lazarus wrote:

Also this thread

Great point. I've merged the two threads.
And I definitely agree this is a "Wow" system. Great find, and very illuminating. Looks like hot Jupiters may indeed start out misaligned.

A couple follow-up papers.

Revisiting a gravity-darkened and precessing planetary system PTFO 8-8695: spin-orbit non-synchronous case
http://arxiv.org/abs/1506.04829

Quote :

We reanalyse the time-variable lightcurves of the transiting planetary system PTFO 8-8695, in which a planet of 3 to 4 Jupiter mass orbits around a rapidly rotating pre-main-sequence star. Both the planetary orbital period of 0.448 days and the stellar spin period less than 0.671 days are unusually short, which makes PTFO 8-8695 an ideal system to check the model of gravity darkening and nodal precession. While the previous analysis of PTFO 8-8695 assumed that the stellar spin and planetary orbital periods are the same, we extend the analysis by discarding the spin-orbit synchronous condition, and find three different classes of solutions roughly corresponding to the nodal precession periods of 199±16, 475±21, and 827±53 days that reproduce the transit lightcurves observed in 2009 and 2010. We compare the predicted lightcurves of the three solutions against the photometry data of a few percent accuracy obtained at Koyama Astronomical Observatory in 2014 and 2015, and find that the solution with the precession period of 199±16 days is preferred even though preliminary. Future prospect and implications to other transiting systems are briefly discussed.

Follow-Up Observations of PTFO 8-8695: A 3 MYr Old T-Tauri Star Hosting a Jupiter-mass Planetary Candidate
http://arxiv.org/abs/1506.08719

Quote :

We present Spitzer 4.5\micron\ light curve observations, Keck NIRSPEC radial velocity observations, and LCOGT optical light curve observations of PTFO~8-8695, which may host a Jupiter-sized planet in a very short orbital period (0.45 days). Previous work by \citet{vaneyken12} and \citet{barnes13} predicts that the stellar rotation axis and the planetary orbital plane should precess with a period of 300−600 days. As a consequence, the observed transits should change shape and depth, disappear, and reappear with the precession. Our observations indicate the long-term presence of the transit events (>3 years), and that the transits indeed do change depth, disappear and reappear. The Spitzer observations and the NIRSPEC radial velocity observations (with contemporaneous LCOGT optical light curve data) are consistent with the predicted transit times and depths for the M⋆=0.34 M⊙ precession model and demonstrate the disappearance of the transits. An LCOGT optical light curve shows that the transits do reappear approximately 1 year later. The observed transits occur at the times predicted by a straight-forward propagation of the transit ephemeris. The precession model correctly predicts the depth and time of the Spitzer transit and the lack of a transit at the time of the NIRSPEC radial velocity observations. However, the precession model predicts the return of the transits approximately 1 month later than observed by LCOGT. Overall, the data are suggestive that the planetary interpretation of the observed transit events may indeed be correct, but the precession model and data are currently insufficient to confirm firmly the planetary status of PTFO~8-8695b.

The thing isn't acting like a planet. No Rossiter-McLaughlin effect detection. Dimming paterns break from predictions. Looks like starspots are a better explanation. http://arxiv.org/abs/1509.02176

YETI observations of the young transiting planet candidate CVSO 30 b
http://arxiv.org/abs/1605.05091

Quote :

CVSO 30 is a unique young low-mass system, because, for the first time, a close-in transiting and a wide directly imaged planet candidates are found around a common host star. The inner companion, CVSO 30 b, is the first possible young transiting planet orbiting a previously known weak-lined T-Tauri star. With five telescopes of the 'Young Exoplanet Transit Initiative' (YETI) located in Asia, Europe and South America we monitored CVSO 30 over three years in a total of 144 nights and detected 33 fading events. In two more seasons we carried out follow-up observations with three telescopes. We can confirm that there is a change in the shape of the fading event between different observations and that the fading event even disappears and reappears. A total of 38 fading event light curves were simultaneously modelled. We derived the planetary, stellar, and geometrical properties of the system and found them slightly smaller but in agreement with the values from the discovery paper. The period of the fading event was found to be 1.36 s shorter and 100 times more precise than the previous published value. If CVSO 30 b would be a giant planet on a precessing orbit, which we cannot confirm, yet, the precession period may be shorter than previously thought. But if confirmed as a planet it would be the youngest transiting planet ever detected and will provide important constraints on planet formation and migration time-scales.

Direct Imaging discovery of a second planet candidate around the possibly transiting planet host CVSO 30
http://arxiv.org/abs/1605.05315

Quote :

We surveyed the 25 Ori association for direct-imaging companions. This association has an age of only few million years. Among other targets, we observed CVSO 30, which has recently been identified as the first T Tauri star found to host a transiting planet candidate. We report on photometric and spectroscopic high-contrast observations with the Very Large Telescope, the Keck telescopes, and the Calar Alto observatory. They reveal a directly imaged planet candidate close to the young M3 star CVSO 30. The JHK-band photometry of the newly identified candidate is at better than 1 sigma consistent with late-type giants, early-T and early-M dwarfs, and free-floating planets. Other hypotheses such as galaxies can be excluded at more than 3.5 sigma. A lucky imaging z' photometric detection limit z'= 20.5 mag excludes early-M dwarfs and results in less than 10 MJup for CVSO 30 c if bound. We present spectroscopic observations of the wide companion that imply that the only remaining explanation for the object is that it is the first very young (< 10 Myr) L-T-type planet bound to a star, meaning that it appears bluer than expected as a result of a decreasing cloud opacity at low effective temperatures. Only a planetary spectral model is consistent with the spectroscopy, and we deduce a best-fit mass of 4-5 Jupiter masses (total range 0.6-10.2 Jupiter masses). This means that CVSO 30 is the first system in which both a close-in and a wide planet candidate are found to have a common host star. The orbits of the two possible planets could not be more different: they have orbital periods of 10.76 hours and about 27000 years. The two orbits may have formed during a mutual catastrophic event of planet-planet scattering.

Same star.

This is such a mess of a system.

Oh goodness you're right. Thanks so much for pointing that out. I'll merge the threads.

H-alpha Variability in PTFO8-8695 and the Possible Direct Detection of Emission from a 2 Million Year Old Evaporating Hot Jupiter
http://arxiv.org/abs/1606.02701

Quote :

We use high time cadence, high spectral resolution optical observations to detect excess H-alpha emission from the 2 - 3 Myr old weak lined T Tauri star PTFO8-8695. This excess emission appears to move in velocity as expected if it were produced by the suspected planetary companion to this young star. The excess emission is not always present, but when it is, the predicted velocity motion is often observed. We have considered the possibility that the observed excess emission is produced by stellar activity (flares), accretion from a disk, or a planetary companion; we find the planetary companion to be the most likely explanation. If this is the case, the strength of the H-alpha line indicates that the emission comes from an extended volume around the planet, likely fed by mass loss from the planet which is expected to be overflowing its Roche lobe.

http://news.rice.edu/2016/06/09/likely-new-planet-may-be-in-slow-death-spiral-2/

Press release (Rice University)

Photo press release about CVSO 30c :
http://www.eso.org/public/france/images/potw1624a/?lang

Another study of the system, coming out against the hot Jupiter explanation for the transit-like events.

Onitsuka et al. "Multi-Color Simultaneous Photometry of the T-Tauri Star Having A Planetary Candidate CVSO 30"
https://arxiv.org/abs/1701.01588

From the conclusion:

Quote :

The wavelength dependence rules out a transiting gas giant scenario because of being too large to be due to a hydrogen-dominated atmosphere of a hot Jupiter or the gravity-darkening effect. In addition, the starspots as a cause of fading events are unlikely because it is difficult for the spots to exist several years near the pole at all times. Thus our result is in favor of transit by circumstellar dust clump or occultation of an accretion hotspot which were introduced by Yu et al. (2015).

Outer planet might be a background star.

Evidence that the planetary candidate CVSO30c is a background star from optical, seeing-limited data
https://arxiv.org/abs/1712.08727

Evidence for planetary hypothesis for PTFO 8-8695b with five-year optical/infrared monitoring observations
https://arxiv.org/abs/2001.00148

Quote :

PTFO 8-8695b (CVSO 30b) is a young planet candidate whose host star is a ∼ 2.6 Myr-old T-Tauri star, and there have been continuous discussions about the nature of this system. To unveil the mystery of this system, we observed PTFO8-8695 for around five years at optical and infrared bands simultaneously using Kanata telescope at the Higashi-Hiroshima Observatory. Through our observations, we found that the reported fading event split into two: deeper but phase-shifted "dip-A" and shallower but equiphase "dip-B". These dips disappeared at different epochs, and then, dip-B reappeared. Based on the observed wavelength dependence of dip depths, a dust clump and a precessing planet are likely origins of dip-A and B, respectively. Here we propose "a precessing planet associated with a dust cloud" scenario for this system. This scenario is consistent with the reported change in the depth of fading events, and even with the reported results, which were thought to be negative evidence to the planetary hypothesis, such as the past non-detection of the Rossiter-McLaughlin effect. If this scenario is correct, this is the third case of a young (<3 Myr) planet around a pre-main sequence star. This finding implies that a planet can be formed within a few Myr.

Maybe not?

PTFO 8-8695: Two Stars, Two Signals, No Planet
https://arxiv.org/abs/2005.10253

First line from the introduction

Quote :

We wish PTFO8-8695b were a planet.

As noted at the end of the conclusion, a similar conclusion was reached independently by Koen (2020).