Dust Clumps in the Protoplanetary Disk of the Young Star GM Cephei

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1 Dust Clumps in the Protoplanetary Disk of the Young Star GM Cephei W. P. Chen( 陳文屏 ), Po-Chieh Huang( 黃柏傑 )(NCU) and the Young Exoplanet Transit Initiative (YETI) Collaboration 星際物理與化學湖南湘潭

2 Stars lose half of their disks within 3 Myr Disks dispersed in ~6 Myr vs planet formation timescale Some exoplanets found, all in the field; statistics suggest ubiquitous planet formation Need data on young planets Haisch

3 Planet formation competes with Disk dissipation in this epoch 1 Myr 10 Myr (Palla, 1993) Class II Disk-bearing classical T Tauri stars Class III Diskless weak line T Tauri stars Nearby young clusters in the transition phase planets in the making

4 YETI- Young Exoplanet Transit Initiative Main goal: to detect possible stellar transits by the youngest exoplanets Method: relay photometric monitoring of young cluster members by a global network of telescopes Byproducts: Stellar variability (periodical, abrupt) YSO accretion activity, rotation, etc.

5 XingJiang Astronomical Observatory (China) Maidanak Observatory (Uzbekistan) Michael Adrian Observatorium (Germany) Nayoro Observatory (Japan) Teide Observatory (Spain) Collaborators: Shuhrat Ehgamberdiev (UBAI), Otabek Burkhonov (UBAI), Johannes M. Ohlert (Stiftung Trebur), Eric Jensen (Swarthmore), Jinzhong Liu (XAO), Hiroyuki Naito (Nayoro), Stefanie Rätz (ESA), Erika Pakstiene (Vilnius U.),

6 An eclipsing star in the Tr-37 field phased to a day orbital period. Data from Jena, Germany, are shown as red (10 s exposures) and green diamonds (60 s), brown plusses from Byurakan, Armenia (60 s), pink crosses from Xinglong, China (10 s), grey stars from Swarthmore, USA (60 s), and pink circles from Lulin, Taiwan (10 s). Follow-up spectroscopy has shown that this star is a double-lined spectroscopic binary (Neuhäuser et al 2011, and AN front cover page).

7 Errmann et al. (2014) Investigation of a transiting planet candidate in Trumpler 37: An astrophysical false positive eclipsing spectroscopic binary star We report our investigation of the first transiting planet candidate from the YETI project in the young ( 4Myr old) open cluster Trumpler 37. The transit-like signal detected in the lightcurve of F8V star 2M repeats every ± days, and has a depth of 54.5± 0.8 mmag in R. Membership in the cluster is supported by its mean radial velocity and location in the color-magnitude diagram, while the Li diagnostic and proper motion are inconclusive in this regard. Follow-up photometric monitoring and adaptive optics imaging allow us to rule out many possible blend scenarios, but our radial-velocity measurements show it to be an eclipsing single-lined spectroscopic binary with a late-type (mid-m) stellar companion, rather than one of planetary nature. The estimated mass of the companion is M. The search for planets around very young stars such as those targeted by the YETI survey remains of critical importance to understand the early stages of planet formation and evolution.

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9 Young Stellar Variability (Herbst et al. 1994) Rotational modulation of cool spots Accretion and rotation of hot spots Variable obscuration by circumstellar dust (UXors) Eruptive YSO Variability FUors brighten up to 6 mag in a few months; followed by a slow decline in years to decades. EXors brighten up to 5 mag in a few months; followed by a fading on about the same time scale.

10 A variety of young stellar variability (Herbig 1977) (Herbig 1977) EX Lup (Hartmann and Kenyon 1996)

11 GM Cephei A UXor in Tr 37 (4 Myr, 900 pc); SpType G7-K0 V Prominent emission lines, IR excess and X-ray emission A CTTS with an active accretion disk, ~10 7 to M yr 1 A very fast rotator, v sin i 43 km s 1 (Sicilia-Aguilar et al., 2008)

12 A century long photometric record intensively after 2009 GM Cep HD (O6.5)

13 Color and Magnitude Behavior Blueing effect seen in all Uxors (e.g., UX Ori, WW Vul) Enhanced scattering during minima (Götz & Wenzel 1968)? Brighter Fainter Bluer Redder

14 Brightness vs. color changes fainter brighter Intermittent, enhanced accretion activity? bluer bluer

15 Orbiting clumps of dust obscure the starlight A YSO disk + a hot accretion zone so as the total brightness drops, the overall color turns blue.

16 Polarization Behavior The star generally polarized P = 4 8%; higher at shorter wavelengths and when fainter. P max at dip minima?

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18 mm on Elias 2-27 (in Rho Oph SFR) optically thin midplane mass + protoplanetary disk 2 symmetric spiral arms and an elliptical ring Peréz+16

19 Conclusion Thus far YETI has not found any exoplanet. The intense monitoring of GM Cep shows that It is a UXor-type variable, with active accretion. Cyclic but not strictly periodical dips suggest a string of dust clumps causing obscuration of the central star. The disk inhomogeneity represents the early phase from grain coagulation to planetesimal formation. Continuing monitoring of the photometric and polarimetric behavior, especially the periodicity evolution, is desirable (+long-wavelength studies) for dust properties.

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22 Lulin Observatory Elevated to 2862m; above the inversion layer seen from Yusan (Jade Mt), the highest peak (4000- m) on the island

23 Lulin One-meter Telescope (LOT) TAOS 4 x 50 cm f/2

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25 NCU/IRCam on UH88 on Maunakea

26 NCUIA NCUIA 64 in 2016