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Young stars and outflows: case studies of three different regions
Stockholm University, Faculty of Science, Department of Astronomy.
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.
Keyword [en]
Star formation, Young stars, Outflows
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-7559ISBN: 978-91-7155-668-4 (print)OAI: oai:DiVA.org:su-7559DiVA: diva2:198596
Public defence
2008-06-04, sal FB53, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Available from: 2008-05-14 Created: 2008-05-14Bibliographically approved
List of papers
1. ISOCAM observations of the L1551 star formation region
Open this publication in new window or tab >>ISOCAM observations of the L1551 star formation region
2004 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 420, no 3, 945- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24961 (URN)
Note
Part of urn:nbn:se:su:diva-7559Available from: 2008-05-14 Created: 2008-05-14Bibliographically approved
2. A detailed study of the L1641N star formation region
Open this publication in new window or tab >>A detailed study of the L1641N star formation region
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.

Keyword
stars: formation -- stars: low-mass, brown dwarfs -- stars: pre-main sequence -- stars: late-type -- infrared: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-24962 (URN)10.1051/0004-6361:20079176 (DOI)
Note
Part of urn:nbn:se:su:diva-7559Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2017-12-13Bibliographically approved
3. Herbig-Haro flows in B335
Open this publication in new window or tab >>Herbig-Haro flows in B335
2007 (English)In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 475, no 1, 281-300 p.Article in journal (Refereed) Published
Abstract [en]

Aims.To study the Herbig-Haro flows in the nearby dark globule B335. To find new HH objects and H2 knots, make a proper motion map of the flow activity and investigate physical properties through shock models. Methods: We have observed optical (Hα and [SII]) and near-IR (2.12 μm H2) deep fields and taken optical spectra using the 2.56 m Nordic Optical Telescope, as well as a near-UV deep field (U band) using the 3.58 m NTT. In addition we present new SPITZER / IRAC (3.5-8.0 μm) and MIPS (24 μm) observations. We use previous Hα and 2.12 μm H2 observations taken 15 and 9 years earlier to make proper motion maps. We then investigate the shock physics by matching our spectra with planar shock models. Results: We discover five new HH objects (HH 119 D-H) in the eastern and one (HH 119 I) in the western lobe of the outflow. From proper motions we find an optically bright, roughly E-W oriented group with high space velocities (200-280 km s-1) and a near-IR bright, slower group (15-75 km s-1) moving to the ESE. We also find a system of at least 15 H2 knots in the western lobe. This (WNW) counterflow suggests the possibility of a binary outflow source, giving rise to two outflow axes with slightly different orientations. We find that the E-W flow is symmetrical with evidence for two outbursts. We make the first detection of [OI] λλ 6300/63 in HH 119 B and Hβ in HH 119 A and B and find their extinctions to be AV ≈ 1.4 and 4.4, respectively. HH 119 A is found to expand much faster than expected from linear expansion with distance from the outflow source. Using planar shock models we find shock velocities of ~60 km s-1 (A) and ~35 km s-1 (B and C). This agrees with A being of higher excitation than B and C. In our U image we detect three of the HH objects and propose that the emission arise from the [OII] λ3728 line and the blue continuum. New SPITZER / IRAC and MIPS observations show most of the HH objects at 4.5 μm and a E-W elongated hour-glass shaped structure at the outflow source. Even at 24 μm it is not clear whether most of the light is direct or reflected.

Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Based on observations made with the New Technology Telescope, ESO (La Silla) under programme ID 077.C-0524. NOT and NTT images in FITS format are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/281

Keyword
ISM: jets and outflows, infrared: ISM, ISM: lines and bands, stars: formation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-24963 (URN)doi:10.1051/0004-6361:20077889 (DOI)
Note
Part of urn:nbn:se:su:diva-7559Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2012-02-14Bibliographically approved
4. Herbig-Haro flows in L1641N
Open this publication in new window or tab >>Herbig-Haro flows in L1641N
2007 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 466, no 2, 579- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24964 (URN)
Note
Part of urn:nbn:se:su:diva-7559Available from: 2008-05-14 Created: 2008-05-14Bibliographically approved

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