XMM-Newton X-Ray Observations of LkCa 15: A T Tauri Star with a Formative Planetary System
- CASA, Univ. of Colorado, Boulder, CO 80309 (United States)
- Dept. of Astronomy, Univ. of Vienna, Türkenschanzstr. 17, A-1180 Vienna (Austria)
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 of ∼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 {sub cool} ≈ 0.4 keV and kT {sub hot} ≈ 2.2 keV. The value of kT {sub 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{sub V} ≈ 1.3–1.7 mag. The intrinsic X-ray luminosity is L {sub x}(0.2–10 keV) = 3 × 10{sup 30} erg s{sup −1}. 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 Σ{sub 0,gas} ∼10{sup 2} g cm{sup −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.
- OSTI ID:
- 22872804
- Journal Information:
- Astrophysical Journal, Vol. 839, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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