Lambda Orionis cluster - Astronomy News

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Date: Nov 12 14:02 2015

Lambda Orionis cluster

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The Lambda Orionis cluster, and miniature 'Belt of Orion'.

Image captured with a 8" f5 Newtonian. Prime focus. Hazy sky.

Lambda Orionis Association (also Collinder 69, Lund 185 and OCl 479.0) is a magnitude +2.8 open star cluster containing about 40 stars located about 1300 ±130 light-years away in the constellation of Orion.
The cluster is very young, forming about five million years ago.

The magnitude +3.4 double star Lambda Orionis (Meissa, the star representing the head of Orion) is the dominant member of the Lambda Orionis cluster, and is located about 1,055 light-years away. The 5.5 magnitude companion is 4.4 arc-seconds to the northwest.
The intense ultraviolet energy radiated by Lambda Orionis creates the Sharpless 264 (Sh2-264, North Orion Bubble) molecular cloud and H II region, which in turn is surrounded by a 200 light-years wide expanding ring of cool gas that has an age of about 2-6 million years
The binary star Phi¹ Orionis (HD 36822), positioned less than a degree to the south of Meissa, is located 1,090 ±90 light-years away.
The orange giant Phi² Orionis (HD 37160) is a forground star located 117 ±1 light-years away.

The cluster was included in the Collinder catalogue published in 1931 by Swedish astronomer Per Collinder

Position(2000): RA 05 35 06.0 Dec +09 56 00

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Date: May 27 20:20 2015

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Title: Is Dust Cloud around lamda Orionis a Ring or a Shell, or Both? Author: Dukhang Lee, Kwang-Il Seon, Young-Soo Jo The dust cloud around lamda Orionis is observed to be circularly symmetric with a large angular extent (\approx 8 degrees). However, whether the three-dimensional (3D) structure of the cloud is shell- or ring-like has not yet been fully resolved. We study the 3D structure using a new approach that combines a 3D Monte Carlo radiative transfer model for ultraviolet (UV) scattered light and an inverse Abel transform, which gives a detailed 3D radial density profile from a two-dimensional column density map of a spherically symmetric cloud. By comparing the radiative transfer models for a spherical shell cloud and that for a ring cloud, we find that only the shell model can reproduce the radial profile of the scattered UV light, observed using the S2/68 UV observation, suggesting a dust shell structure. However, the inverse Abel transform applied to the column density data from the Pan-STARRS1 dust reddening map results in negative values at a certain radius range of the density profile, indicating the existence of additional, non-spherical clouds near the nebular boundary. The additional cloud component is assumed to be of toroidal ring shape; we subtracted from the column density to obtain a positive, radial density profile using the inverse Abel transform. The resulting density structure, composed of a toroidal ring and a spherical shell, is also found to give a good fit to the UV scattered light profile. We therefore conclude that the cloud around lamda Ori is composed of both ring and shell structures. Read more (889kb, PDF) __________________

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Date: Aug 25 21:28 2010

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Title: Spitzer Observations of the Lambda Orionis cluster. II. Disks around solar-type and low mass stars Authors: Jesus Hernandez, Maria Morales-Calderon, Nuria Calvet, L. Hartmann, J. Muzerolle, R. Gutermuth, K. L. Luhman, J. Stauffer We present IRAC/MIPS Spitzer Space Telescope observations of the solar type and the low mass stellar population of the young (~5 Myr) Lambda Orionis cluster. Combining optical and 2MASS photometry, we identify 436 stars as probable members of the cluster. Given the distance (450 pc) and the age of the cluster, our sample ranges in mass from 2 solar mass to objects below the substellar limit. With the addition of the Spitzer mid-infrared data, we have identified 49 stars bearing disks in the stellar cluster. Using spectral energy distribution (SED) slopes, we place objects in several classes: non-excess stars (diskless), stars with optically thick disks, stars with "evolved disks"( with smaller excesses than optically thick disk systems), and "transitional disks" candidates (in which the inner disk is partially or fully cleared). The disk fraction depends on the stellar mass, ranging from ~6% for K type stars (Rc-J<2) to ~27% for stars with spectral type M5 or later (Rc-J>4). We confirm the dependence of disk fraction on stellar mass in this age range found in other studies. Regarding clustering levels, the overall fraction of disks in the Lambda Orionis cluster is similar to those reported in other stellar groups with ages normally quoted as ~5 Myr. Read more (1175kb, PDF) __________________

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