Age Determination Method of Pre-Main Sequence Stars with High-Resolution I-Band Spectroscopy

We present a new method for determining the age of late-K type pre-main sequence (PMS) stars by deriving their surface gravity from high-resolution I-band spectroscopy. Since PMS stars contract as they evolve, age can be estimated from surface gravity. We used the equivalent width ratio (EWR) of nearby absorption lines to create a surface gravity diagnostic of PMS stars that is free of uncertainties due to veiling. The ratios of Fe (818.67nm and 820.49nm) and Na (818.33nm and 819.48nm) absorption lines were calculated for giants, main-sequence stars, and weak-line T Tauri stars. Effective temperatures were nearly equal across the sample. The Fe to Na EWR (Fe/Na) decreases significantly with increasing surface gravity, denoting that Fe/Na is a desirable diagnostic for deriving the surface gravity of pre-main sequence stars. The surface gravity of PMS stars with 0.8 solar mass is able to be determined with an accuracy of 0.1-0.2, which conducts the age of PMS stars within a factor of 1.5, in average.Comment: 16 pages, 5 figures, 3 tables, accepted for publication in PAS

Dust from Comet 209P/LINEAR during its 2014 Return: Parent Body of a New Meteor Shower, the May Camelopardalids

We report a new observation of the Jupiter-family comet 209P/LINEAR during its 2014 return. The comet is recognized as a dust source of a new meteor shower, the May Camelopardalids. 209P/LINEAR was apparently inactive at a heliocentric distance rh = 1.6 au and showed weak activity at rh < 1.4 au. We found an active region of <0.001% of the entire nuclear surface during the comet's dormant phase. An edge-on image suggests that particles up to 1 cm in size (with an uncertainty of factor 3-5) were ejected following a differential power-law size distribution with index q=-3.25+-0.10. We derived a mass loss rate of 2-10 kg/s during the active phase and a total mass of ~5x10^7 kg during the 2014 return. The ejection terminal velocity of millimeter- to centimeter-sized particles was 1-4 m/s, which is comparable to the escape velocity from the nucleus (1.4 m/s). These results imply that such large meteoric particles marginally escaped from the highly dormant comet nucleus via the gas drag force only within a few months of the perihelion passage.Comment: 18 pages, 4 figures, accepted on 2014 December 11 for publication in the Astrophysical Journal Letter

Association between Skeletal Muscle Depletion and Sorafenib Treatment in Male Patients with Hepatocellular Carcinoma: A Retrospective Cohort Study

The effect of skeletal muscle mass (SMM) on the outcomes of sorafenib treatment for hepatocellular carcinoma (HCC) has not been established. We measured the SMM in HCC patients treated with sorafenib, evaluated the patients’ survival, and evaluated the association between skeletal muscle depletion and sorafenib treatment. Of the 97 HCC patients treated with sorafenib at our institution in the period from July 2009 to February 2015, our study included 69 patients (51 males, 18 females) who had received sorafenib for ≥ 8 weeks and whose follow-up data were available. SMM was calculated from computed tomography images at the mid-L3 level (cm2) and normalized to height (m2) to yield the L3 skeletal muscle index (L3-SMI, cm2/m2). The median L3-SMI value was higher in the males (43 cm2/m2) compared to the females (36 cm2/m2). In the males only, the multivariate Cox regression identified an L3-SMI <43 cm2/m2 as independently associated with higher mortality compared to an L3-SMI ≥43 cm2/m2 (hazard ratio 2.315, 95% confidence interval: 1.125-4.765, p=0.023). Skeletal muscle depletion is a factor predicting poor prognosis for male patients with advanced HCC treated with sorafenib