Near-infrared imaging polarimetry of LkCa 15: A possible warped inner disk

Oh, Deog‐Hwan; Hashimoto, Jun; Tamura, Motohide; Wisniewski, John P.; Akiyama, Eiji; Currie, Thayne; Mayama, Satoshi; Miki, Takami; Thalmann, Christian; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, W.; Brandt, Timothy D.; Carson, J.; Egner, Sebastian; Feldt, M.; Goto, Miwa; Grady, C. A.; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, G. R.; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken M.; Morino, Jun Ichi; Moro‐Martín, Amaya; Nishimura, Tetsuo; Pyo, Tae‐Soo; Serabyn, Eugene; Suenaga, Takuya; Shimada, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro; Takato, Naruhisa; Terada, Hiroshi; Turner, Edwin L.; Watanabe, Makoto; Yamada, Tōru; Takami, Hideki; Usuda, Tomonori

doi:10.1093/pasj/psv133

Cited by 20 publications

(15 citation statements)

References 30 publications

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“…The inner Gaussian (central disk) component in our model has a FWHM ∼5 au, the radii of the inner and outer polar Gaussian rings in our model are ∼17 au and ∼45 au, respectively, with an inclination of ∼45 degrees. On scales of the inner and outer rings, our model is mostly consistent with what has been previously quantified at similar wavelengths using direct or coronagraphic imaging by Thalmann et al (2014Thalmann et al ( , 2015Thalmann et al ( , 2016, Oh et al (2016) and Currie et al (2019). The compact central Gaussian disk of our three component model is near the smallest angular scales that we expect to be able to observe with our SAM measurements.…”

Section: Comparing Disk Image Reconstructionssupporting

confidence: 89%

“…An outer disk, beyond the arc seen in the single polar Gaussian ring model, has been observed previously at similar wavelengths to our data (e.g. Thalmann et al 2014;Oh et al 2016;Currie et al 2019). The bright inner edge of this outer disk component resides at an angular scale which the present SAM observations can probe and therefore should contribute a non-negligible amount to our visibility measurements.…”

Section: Direct Image Reconstructionsupporting

confidence: 88%

“…To help avoid issues with potential degeneracy between the radius and inclination of our ring models, the inclination of LkCa 15 is constrained to be between 40 and 60 degrees, as LkCa 15 is known to have a moderately inclined disk on the sky (e.g. Thalmann et al 2014;Oh et al 2016). All other parameters are constrained only to be physically realistic.…”

Section: Direct Image Reconstructionmentioning

confidence: 99%

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Two Rings and a Marginally Resolved, 5 AU, Disk Around LkCa 15 Identified Via Near Infrared Sparse Aperture Masking Interferometry

Blakely,

Francis,

Johnstone

et al. 2022

Preprint

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Sparse aperture masking interferometry (SAM) is a high resolution observing technique that allows for imaging at and beyond a telescope's diffraction limit. The technique is ideal for searching for stellar companions at small separations from their host star; however, previous analysis of SAM observations of young stars surrounded by dusty disks have had difficulties disentangling planet and extended disk emission. We analyse VLT/SPHERE-IRDIS SAM observations of the transition disk LkCa 15, model the extended disk emission, probe for planets at small separations, and improve contrast limits for planets. We fit geometrical models directly to the interferometric observables and recover previously observed extended disk emission. We use dynamic nested sampling to estimate uncertainties on our model parameters and to calculate evidences to perform model comparison. We compare our extended disk emission models against point source models to robustly conclude that the system is dominated by extended emission within 50 au. We report detections of two previously observed asymmetric rings at ∼17 au and ∼45 au. The peak brightness location of each model ring is consistent with the previous observations. We also, for the first time with imaging, robustly recover an elliptical Gaussian inner disk, previously inferred via SED fitting. This inner disk has a FWHM of 5 au and a similar inclination and orientation as the outer rings. Finally, we recover no clear evidence for candidate planets. By modelling the extended disk emission, we are able to place a lower limit on the near infrared companion contrast of at least 1000.

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Section: Comparing Disk Image Reconstructionssupporting

confidence: 89%

Section: Direct Image Reconstructionsupporting

confidence: 88%

Section: Direct Image Reconstructionmentioning

confidence: 99%

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Two Rings and a Marginally Resolved, 5 AU, Disk Around LkCa 15 Identified Via Near Infrared Sparse Aperture Masking Interferometry

Blakely,

Francis,

Johnstone

et al. 2022

Preprint

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“…Whereas this remains compatible with the inclination angle of the outer disc (≃50 • , Thalmann et al 2014;van der Marel et al 2015), our tomographic modeling (see Sec. 4) suggests that i needs to be at least 70 • to ensure an optimal fit to the spectropolarimetric data, implying that the inner disc is likely warped as already suggested by previous studies (Oh et al 2016). This is also supported by the fact that LkCa 15 is a periodic 'dipper' (Alencar et al 2018), with the inner disc warp regularly occulting the star as it rotates, and requiring i to be within 70 − 90 • (Cody & Hillenbrand 2018).…”

Section: Evolutionary Status Of Lkca 15mentioning

confidence: 69%

“…This can be achieved using phase-resolved spectropolarimetric observations coupled to tomographic imaging techniques inspired from medical imaging (e.g., Donati et al 2006;Donati & Landstreet 2009). In this paper, we study the well known cTTS LkCa 15, whose accretion disc, called a transition disc from the fact that it features a wide dust gap from the inner disc up to 50 au from the central star, is reported to be potentially warped (Oh et al 2016) with claims of ongoing planet formation (Kraus & Ireland 2012;Sallum et al 2015, later challenged by Thalmann et al 2015Mendigutía et al 2018). Whereas our paper concentrates on the magnetic field of LkCa 15, a companion study focusses on the properties of its inner accretion disc (Alencar et al 2018).…”

Section: Introductionmentioning

confidence: 99%

The magnetic propeller accretion regime of LkCa 15

Donati

Bouvier

Alencar

et al. 2018

Monthly Notices of the Royal Astronomical Society: Letters

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We present a spectropolarimetric study of the classical T Tauri star (cTTS) LkCa 15 investigating the large-scale magnetic topology of the central star and the way the field connects to the inner regions of the accretion disc. We find that the star hosts a strong poloidal field with a mainly axisymmetric dipole component of 1.35 kG, whereas the mass accretion rate at the surface of the star is 10 −9.2 M ⊙ yr −1 . It implies that the magnetic field of LkCa 15 is able to evacuate the central regions of the disc up to a distance of 0.07 au at which the Keplerian orbital period equals the stellar rotation period. Our results suggest that LkCa 15, like the lower-mass cTTS AA Tau, interacts with its disc in a propeller mode, a regime supposedly very efficient at slowing down the rotation of cTTSs hosting strong dipolar fields.

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Spectro-astrometry of the pre-transitional star LkCa 15 does not reveal an accreting planet but extended Hα emission

Mendigutía

Oudmaijer

Schneider

et al. 2018

A&A

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Context. The detection of forming planets in protoplanetary disks around young stars remains elusive, and state-of-the-art observational techniques provide somewhat ambiguous results. The pre-transitional T Tauri star LkCa 15 is an excellent example. It has been reported that it could host three planets; candidate planet b is in the process of formation, as inferred from its Hα emission. However, a more recent work casts doubts on the planetary nature of the previous detections. Aims. We test the potential of spectro-astrometry in Hα as an alternative observational technique to detect forming planets around young stars, taking LkCa 15 as a reference case Methods. LkCa 15 was observed with the ISIS spectrograph at the 4.2m William Herschel Telescope (WHT). The slit was oriented towards the last reported position of LkCa 15 b (parallel direction) and 90 • from that (perpendicular). The photocenter and full width half maximum (FWHM) of the Gaussians fitting the spatial distribution at Hα and the adjacent continuum were measured. A well-known binary (GU CMa) was used as a calibrator to test the spectro-astrometric performance of ISIS/WHT. Results. A consistent spectro-astrometric signature is recovered for GU CMa. However, the photocenter shift predicted for LkCa 15 b is not detected, but the FWHM in Hα is broader than in the continuum for both slit positions. Our simulations show that the photocenter and FWHM observations cannot be explained simultaneously by an accreting planet, but the lack of photocenter shift alone could still be consistent with an emitting planet with contrast 5.5 mags in Hα or 6 mag in the adjacent continuum. In turn, both spectro-astrometric observations are naturally reproduced from a roughly symmetric Hα emitting region centered on the star and extent comparable to the orbit originally attributed to the planet at several au. Conclusions. The extended Hα emission around LkCa 15 could be related to a variable disk wind, but additional multi-epoch data and detailed modeling are necessary to understand its physical nature. Optical spectro-astrometry carried out with mid-size telescopes is capable of probing small-scale structures in relatively faint young stars that are not easily accessible with state-of-the-art instrumentation mounted on larger telescopes. Therefore, spectro-astrometry in Hα is able to test the presence of accreting planets and can be used as a complementary technique to survey planet formation in circumstellar disks.

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Near-infrared imaging polarimetry of LkCa 15: A possible warped inner disk

Cited by 20 publications

References 30 publications

Two Rings and a Marginally Resolved, 5 AU, Disk Around LkCa 15 Identified Via Near Infrared Sparse Aperture Masking Interferometry

Two Rings and a Marginally Resolved, 5 AU, Disk Around LkCa 15 Identified Via Near Infrared Sparse Aperture Masking Interferometry

The magnetic propeller accretion regime of LkCa 15

Spectro-astrometry of the pre-transitional star LkCa 15 does not reveal an accreting planet but extended Hα emission

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