XMM-Newton X-ray Observations of LkCa 15: A T Tauri Star With a Formative Planetary System

Abstract

High-resolution ground-based images of the T Tauri star LkCa 15 have revealed multiple companions that are thought to comprise a formative planetary system. The candidate protoplanets orbit at distances ~15 - 20 AU within the dust-depleted inner region of the circumstellar disk. Because of its young age (1 - 4 Myr), LkCa 15 provides a benchmark system for testing planet-formation models. We detected LkCa 15 as a bright X-ray source in a short 10 ks Chandra observation in 2009. We report here new results obtained from a deeper 37 ks XMM-Newton observation in 2014. The new data provide better sampling in the time domain and improved sensitivity at low energies below 1 keV. Spectral fits with thermal emission models require at least two temperature components at kT_cool ~ 0.4 keV and kT_hot ~ 2.2 keV. The value of kT_hot is about a factor of two less than inferred from Chandra, suggesting that the hot-component temperature is variable. The best-fit absorption column density is in good agreement with that expected from optical extinction estimates A_v = 1.3 - 1.7 mag. The intrinsic X-ray luminosity is L_x(0.2 - 10 keV) = 3e30 ergs/s. Estimates of the X-ray heating rate of the inner disk and protoplanets are sensitive to the assumed disk gas surface density for which recent ALMA observations give estimates Sigma_0(gas) ~ 100 g/cm^2 at 1 AU from the star. At such densities, X-ray heating is confined mainly to the upper disk layers and X-ray penetration through the disk midplane to the protoplanets at r ~ 15 - 20 AU is negligible.

20 pages, 6 figures, 3 tables

References in corpus (11)

• The Catalina Surveys Periodic Variable Star Catalog
• The XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST)
• Accreting Protoplanets in the LkCa 15 Transition Disk
• Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA
• On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds
• X-ray Emission from T Tauri Stars and the Role of Accretion: Inferences from the XMM-Newton Extended Survey of the Taurus Molecular Cloud
• Searching for circumplanetary disks around LkCa 15
• Resolving the planet-hosting inner regions of the LkCa 15 disk
• The architecture of the LkCa 15 transitional disk revealed by high-contrast imaging
• Spectral properties of X-ray bright variable sources in the Taurus Molecular Cloud
• Coronal abundances of X-ray bright pre-main sequence stars in the Taurus Molecular Cloud

Cited by in corpus (4)

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• Spectro-astrometry of the pre-transitional star LkCa 15 does not reveal an accreting planet but extended H$\alpha$ emission
• X-ray and UV radiation in the planet-forming T-Tauri system PDS 70. Signs of accretion and coronal activity
• Chandra X-ray Observations of V830 Tau: A T Tauri Star Hosting an Evanescent Planet