Change search
ReferencesLink to record
Permanent link

Direct link
A detailed study of the L1641N star formation region
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
2008 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 489, no 3, 1409-1439 p.Article in journal (Refereed) Published
Abstract [en]

Aims. We search for young stellar objects (YSOs) in the L1641N cluster and characterize the star formation activity through determination of the age distribution, mass function, spatial distribution, and the star formation history.Methods. Multi-wavelength broad band photometry both from space and the ground are used to look for IR excess in order to separate field stars from YSOs and to sample the spectral energy distributions. Space-based observations were obtained using the ISO satellite (ISOCAM) in two filters, centred at 6.7 and 14.3 m, and Spitzer (IRAC) at 3.6, 4.5, 5.8, and 8.0 m. Our ground-based observations were made with the Nordic Optical Telescope (NOT) using ALFOSC (I band), NOTCam (J, and 2.12 m H2), and SIRCA (L'). More than 50 of the brightest I-band sources were then studied with follow-up optical spectroscopy (5780-8340 Å) to check for signs of accretion (H in emission) and youth (Li I

in absorption) and to determine their effective temperatures. By comparing theoretical evolution tracks with our YSO sample in the H-R diagram, we calculated an age, luminosity, and mass distribution.Results. We detect a total of 216 (Spitzer or I band) sources in L1641N, 89 of which are YSO candidates. Most of the spectra are of M-type with H strongly in emission, and many have Li 6707 in absorption. The four brightest I band sources (F and G stars) are suggested as foreground stars, and the L1641N IRAS source is shown to be the combined flux of at least four sources. We find that the interstellar extinction is well-fit in the optical and near-IR by a power law with an exponent of 1.58, although in the mid-IR the Spitzer observations show a higher extinction than expected from theory. The median age of the YSO sample is ~1 Myr and the resulting MF has a flat distribution for low masses down to the completeness limit. There is evidence of a constant star formation rate of one star in 3.7  104 yr during the past few Myr. We find 11 sources older than 10 Myr and a spatial separation between younger and older YSOs, suggesting that many of the older stars formed in L1641N could have left the cluster, giving the appearance of an increased star formation rate with time.

Place, publisher, year, edition, pages
2008. Vol. 489, no 3, 1409-1439 p.
Keyword [en]
stars: formation -- stars: low-mass, brown dwarfs -- stars: pre-main sequence -- stars: late-type -- infrared: stars
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-24962DOI: 10.1051/0004-6361:20079176OAI: diva2:198593
Part of urn:nbn:se:su:diva-7559Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2011-02-07Bibliographically approved
In thesis
1. Young stars and outflows: case studies of three different regions
Open this publication in new window or tab >>Young stars and outflows: case studies of three different regions
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mass is clearly the most important parameter of a star as it determines the phases it will go through, its physical parameters, the elements produced and its life span. Two important processes that occur simultaneously in young stars are directly related to the final mass a star ends up with; the accretion of material onto the star from a circumstellar disk and the bipolar outflow of material from the star. These processes are related since the infalling material drives the outflow. The life span of circumstellar disks is also important for the possibility of life, as this limits the time available for planet formation. This may depend on the stellar mass and its environment.

Three detailed observational case-studies are presented, a globule (B335) that is forming only one or two stars, a medium-sized star formation region (L1551) and a large cluster of young stars (YSOs) in a part of our nearest giant molecular cloud (L1641N).

The first part of this thesis concerns finding YSOs by looking for mid-IR excess, indicative of circumstellar disks, using the ISO and Spitzer satellites in combination with ground-based observations. Other signs of youth are also used; H-alpha in emission (accretion), Li 6707 in absorption (Li is destroyed with age) and cloud membership based on extinction. The detection of 15 new YSO candidates in L1551 (Paper I) and 89 YSOs in L1641N (Paper II) is presented. In L1641N, distributions are presented of stellar age and mass. An empirical extinction law is found and the star formation history is presented. There seems to be an accelerated star formation with time. This can however also be explained, at least partly, by migration of older stars from the cluster - a migration that may very well be mass dependent.

The second part concerns bipolar outflows. The discovery of six Herbig-Haro objects and at least 15 H2 objects in B335 is presented (Paper III) as well as proper motions for previously known objects. A planar shock model is used to calculate shock velocities. In L1641N (Paper IV) we discover a new outflow source and connect this to a number of H2 objects that are found to be part of this flow from proper motion measurements.

Place, publisher, year, edition, pages
Stockholm: Institutionen för astronomi, 2008. 91 p.
Star formation, Young stars, Outflows
National Category
Astronomy, Astrophysics and Cosmology
Research subject
urn:nbn:se:su:diva-7559 (URN)978-91-7155-668-4 (ISBN)
Public defence
2008-06-04, sal FB53, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Available from: 2008-05-14 Created: 2008-05-14Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Olofsson, Göran
By organisation
Department of Astronomy
In the same journal
Astronomy and Astrophysics
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 29 hits
ReferencesLink to record
Permanent link

Direct link