3 research outputs found
Photometric and Spectroscopic Analysis of Young, Nearby Open Cluster Collinder 70
We present the results of a wide-field (80’ x 80’) photometric and spectroscopic survey of the young open cluster Collinder 70, which is also known as the ORI OB 1b association, centered on the central star of Orion’s belt, ε Ori (Alnilam). Seventy Coll 70 spectroscopy targets were selected from BVRIc color magnitude diagrams for observation using the CTIO HYDRA multi-object spectrograph; we aimed to identify targets exhibiting H in emission and a strong lithium 6708Å line in absorption. About a third of our targets (23/70 stars) are consistent with being youthful members of Coll 70. Intermediate resolution (R!20000) HYDRA Li I 6708Å equivalent widths and Baraffe et al. (2002) evolutionary models strongly suggest that this association is \u3c\u3c 30 Myr. Observational evidence showing that some stars exhibit primordial levels of lithium, giant-like features in low-resolution spectra and the presence of infra-red excesses indicate that the association is considerably younger than 30 Myr and is a potentially valuable target for age determination using the Lithium Depletion Boundary method
The Neutral Gas Dynamics of the Nearby Magellanic Irregular Galaxy UGCA 105
We present new low-resolution HI spectral line imaging, obtained with the
Karl G. Jansky Very Large Array (JVLA), of the star-forming Magellanic
irregular galaxy UGCA 105. This nearby (D = 3.39+/-0.25 Mpc), low mass
[M_HI=(4.3+/-0.5)x10^8 Solar masses] system harbors a large neutral gas disk
(HI radius ~7.2 kpc at the N_HI=10^20 cm^-2 level) that is roughly twice as
large as the stellar disk at the B-band R_25 isophote. We explore the neutral
gas dynamics of this system, fitting tilted ring models in order to extract a
well-sampled rotation curve. The rotation velocity rises in the inner disk,
flattens at 72+/-3 km/s, and remains flat to the last measured point of the
disk (~7.5 kpc). The dynamical mass of UGCA 105 at this outermost point,
(9+/-2)x10^9 Solar masses, is ~10 times as large as the luminous baryonic
components (neutral atomic gas and stars). The proximity and favorable
inclination (55 degrees) of UGCA 105 make it a promising target for
high-resolution studies of both star formation and rotational dynamics in a
nearby low-mass galaxy.Comment: The Astronomical Journal, in pres