Rotation alignment in neutron-rich Cr isotopes: A probe of deformed single-particle levels across N=40

Recent experiments have reached the neutron-rich Cr isotope with N=40 and confirmed enhanced collectivity near this sub-shell. The current data focus on low-spin spectroscopy only, with little information on the states where high-j particles align their spins with the system rotation. By applying the Projected Shell Model, we show that rotation alignment occurs in neutron-rich even-even Cr nuclei as early as spin 8 and, due to shell filling, the aligning particles differ in different isotopes. It is suggested that observation of irregularities in moments of inertia is a direct probe of the deformed single-particle scheme in this exotic mass region.Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev.

Mass Estimates of a Giant Planet in a Protoplanetary Disk from the Gap Structures

A giant planet embedded in a protoplanetary disk forms a gap. An analytic relationship among the gap depth, planet mass $M_{p}$, disk aspect ratio $h_p$, and viscosity $\alpha$ has been found recently, and the gap depth can be written in terms of a single parameter $K= (M_{p}/M_{\ast})^2 h_p^{-5} \alpha^{-1}$. We discuss how observed gap features can be used to constrain the disk and/or planet parameters based on the analytic formula for the gap depth. The constraint on the disk aspect ratio is critical in determining the planet mass so the combination of the observations of the temperature and the image can provide a constraint on the planet mass. We apply the formula for the gap depth to observations of HL~Tau and HD~169142. In the case of HL~Tau, we propose that a planet with $\gtrsim 0.3$ is responsible for the observed gap at $30$~AU from the central star based on the estimate that the gap depth is $\lesssim 1/3$. In the case of HD~169142, the planet mass that causes the gap structure recently found by VLA is $\gtrsim 0.4 M_J$. We also argue that the spiral structure, if observed, can be used to estimate the lower limit of the disk aspect ratio and the planet mass.Comment: 16 pages, 5 figures, accepted for publication in The Astrophysical Journal Letter

High Angular Resolution, Sensitive CS J=2-1 and J=3-2 Imaging of the Protostar L1551 NE: Evidence for Outflow-Triggered Star Formation ?

High angular resolution and sensitive aperture synthesis observations of CS ($J=2-1$) and CS ($J=3-2$) emissions toward L1551 NE, the second brightest protostar in the Taurus Molecular Cloud, made with the Nobeyama Millimeter Array are presented. L1551 NE is categorized as a class 0 object deeply embedded in the red-shifted outflow lobe of L1551 IRS 5. Previous studies of the L1551 NE region in CS emission revealed the presence of shell-like components open toward L1551 IRS 5, which seem to trace low-velocity shocks in the swept-up shell driven by the outflow from L1551 IRS 5. In this study, significant CS emission around L1551 NE was detected at the eastern tip of the swept-up shell from $V_{\rm{lsr}}$ = 5.3 km s$^{-1}$ to 10.1 km s$^{-1}$, and the total mass of the dense gas is estimated to be 0.18 $\pm$ 0.02 $M_\odot$. Additionally, the following new structures were successfully revealed: a compact disklike component with a size of $\approx$ 1000 AU just at L1551 NE, an arc-shaped structure around L1551 NE, open toward L1551 NE, with a size of $\sim 5000$ AU, i.e., a bow shock, and a distinct velocity gradient of the dense gas, i.e., deceleration along the outflow axis of L1551 IRS 5. These features suggest that the CS emission traces the post-shocked region where the dense gas associated with L1551 NE and the swept-up shell of the outflow from L1551 IRS 5 interact. Since the age of L1551 NE is comparable to the timescale of the interaction, it is plausible that the formation of L1551 NE was induced by the outflow impact. The compact structure of L1551 NE with a tiny envelope was also revealed, suggesting that the outer envelope of L1551 NE has been blown off by the outflow from L1551 IRS 5.Comment: 29 pages, 12 figures, Accepted for Publication in the Astrophysical Journa