NATURAL CORONAGRAPHIC OBSERVATIONS OF THE ECLIPSING T TAURI SYSTEM KH 15D: EVIDENCE OF ACCRETION AND BIPOLAR OUTFLOW IN A WEAK-LINE T TAURI STAR

摘要

We present high-resolution (R ～ 44,000) UV-Visual Echelle Spectrograph spectra of the eclipsing pre-main-sequence star KH 15D covering the wavelength range 4780-6810 A obtained at three phases: out of eclipse, near minimum light, and during egress. The system evidently acts as a natural coronagraph, enhancing the contrast relative to the continuum of hydrogen and forbidden emission lines during eclipse. At maximum light, the Hα equivalent width was ～2 A and the profile showed broad wings and a deep central absorption. During egress, the equivalent width was much higher (～70 A) and the broad wings, which extend to +-300 km s~(-1), were prominent. During eclipse totality, the equivalent width was less than during egress (～40 A) and the high-velocity wings were much weaker. Hβ showed a somewhat different behavior, revealing only the blueshifted portion of the high-velocity component during eclipse and egress. [O Ⅰ] λλ6300, 6363 lines are easily seen both out of eclipse and when the photosphere is obscured and exhibit little or no flux variation with the eclipse phase. Our interpretation is that KH 15D, although clearly a weak-line T Tauri star by the usual criteria, is still accreting matter from a circumstellar disk and has a well-collimated bipolar jet. As the knife-edge of the occulting matter passes across the close stellar environment, it is evidently revealing structure in the magnetosphere of this pre-main-sequence star with unprecedented spatial resolution. We also show that there is only a small, perhaps marginally significant change in the velocity of the K7 star between the maximum light and egress phases probed here.