DOCSLIB.ORG

Young Stellar Objects in the Orion B Cloud

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Young Stellar Objects in the Orion B Cloud Astronomical Science Young Stellar Objects in the Orion B Cloud Monika G. Petr-Gotzens1 Juan M. Alcalá2 1 Loredana Spezzi1,3 Jes K. Jørgensen4 ( Thomas Stanke1 Marco Lombardi5,6 João F. Alves7 1 ESO 2 INAF Osservatorio Astronomico di Capodimonte, Napoli, Italy 3 European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), Darmstadt, Germany 4 Niels Bohr Institute, University of Copenhagen, Denmark 5 Department of Physics, University of Milan, Italy 6 Harvard-Smithsonian Center for Astrophysics, Cambridge, USA 7 Department of Astrophysics, University of Vienna, Austria Wide-field near-infrared imaging sur- veys offer an excellent opportunity to obtain spatially complete samples of young stars in nearby star-forming regions. By studying their spatial distri- bution and individual properties, the global star formation characteristics of a region can be established. Near-infra- red wide-field imaging observations of a significantly large area in the Orion Molecular Cloud B, obtained with the VISTA telescope on Cerro Paranal are presented. On the basis of photometric selection criteria, we have identified 186 candidate young stellar objects that are associated with the stellar clusters NGC 2068 and NGC 2071, and with the stellar group around HH24-26. Overall, Orion B shows a lot of similarities in its star formation characteristics with other Galactic star-forming regions: a star formation efficiency of a few percent, a equator. Orion is also the nearest region Figure 1. VISTA three-colour (ZJKs) mosaic image of stellar mass distribution very similar of active high- and low-mass star for- the northern part of Orion B on a logarithmic display. The image covers ~ 1.6 square degree and contains to that of the Orion Trapezium cluster, mation allowing us to study many aspects more than 100 000 objects. Clearly visible in the and a high observed fraction of circum- of the star formation process in great north is the embedded stellar cluster NGC 2071, stellar discs. detail. while the cluster in the centre is NGC 2068. For the study presented here, we ana- Orion mini-survey (Petr-Gotzens et al., VISTA wide-field observations of Orion B lysed the multi-band photometry of a 2011). The analysed field contains the ~ 1.6 square degree field in the northern prominent bright optical reflection nebu- The constellation of Orion is a beautiful part of the Orion Molecular Cloud B, losities NGC 2068 and NGC 2071 which, night-sky object visible to both southern which was observed as part of the Visible observed at near-infrared wavelengths, and northern hemisphere skywatchers, and Infrared Survey Telescope for Astron- beautifully reveal their full nature as due to its location close to the celestial omy (VISTA) Science Verification (SV) young stellar clusters (Figure 1). The ages 42 The Messenger 162 – December 2015 Figure 2. Upper four 4 4 Selection of young stellar objects L1630N SWIRE/resamp [2.58 deg2 ] panels: VISTA/Spitzer 6 6 colour– magnitude diagrams for objects The region of Orion B that we studied 8 8 in Orion B. The dot– contains roughly 160 000 VISTA sources, ] ] dashed lines show among which less than 1% (!) are actually .5 10 .5 10 [4 [4 fuzzy limits with expo- young objects belonging to Orion; the 12 12 nential cutoffs that define the YSO can- large majority of the sources are fore- 14 14 didate selection criterion ground and background stars. Efficient in each diagram, and reliable young stellar object (YSO) 16 16 excluding contamination source selection is therefore a critical 01234 01234 from galaxies (dia- [4.5]–[8.0] [4.5]–[8.0] monds) and field stars task. We employ a multicolour selection presenting normal method that is based on the combination 0 0 photospheric colours of JHKs near-infrared photometry with (black circles). The con- that in the mid-infrared, and has been 2 2 tinuous red lines show proven to provide an optimal distinction 4 4 hard limits; fainter 0] 0] objects are excluded between disc-bearing young stellar 4. 4. [2 6 [2 6 from the YSO category. objects, reddened field stars and galaxies Point-like and extended (Harvey et al., 2007). In detail, the location 8 8 YSO candidates are indicated by red dots of an object in each of the colour–colour 10 10 and open squares, and colour–magnitude diagrams is com- respectively; YSO can- 12 12 pared with well-defined boundaries in didates with no VISTA these diagrams for the expected loca- 02468 02468 morphological classifi- [4.5]–[8.0] [4.5]–[8.0] cation are indicated by tions of young stellar objects (Figure 2). asterisks. The selection is then decided on a com- 0 0 bined probability for a source being a Lower four panels: young stellar object, based on its location 2 2 2MASS/Spitzer colour– magnitude and colour– in colour–colour and colour–magnitude 4 4 colour diagrams for the space. 0] 0] 4. 4. SWIRE galaxy cata- [2 6 [2 6 logue. Three objects This selection method has been applied from the SWIRE cata- 8 8 logue (marked as aster- very successfully to select YSO candi- isks) are classified as dates in star-forming regions observed 10 10 YSO candidates, within the Spitzer c2d and Spitzer Gould 12 12 according to our selec- Belt legacy surveys (e.g., Evans et al., tion criteria. 01234 01234 2009; Hatchell et al., 2012). In order to [4.5]–[8.0] [4.5]–[8.0] apply the same method, we matched our VISTA catalogue with the Spitzer com- bined Infrared Array Camera (IRAC) and 3 3 Multi-Band Imaging Photometer (MIPS) 2 2 catalogue by Megeath et al. (2012), K K resulting in ~ 58 500 sources with com- H– H– 1 1 plete ZYJHKs, IRAC 3.6, 4.5, 5.8 and 8 μm and MIPS-24 μm photometry. Fig- 0 0 ure 2 shows the VISTA/Spitzer colour– colour and colour–magnitude diagrams used to select the YSO candidates in 0123401234 K–[4.5] K–[4.5] Orion B, which led to a total number of 188 such candidates that are indicated in of the clusters have been determined J ~ 20.3 mag and Z ~ 22.5 mag. All data Figure 2 with red symbols. by Flaherty & Muzerolle (2008) to be reduction was performed by the Cam- 1–2 Myr, although star formation appears bridge Astronomy Survey Unit (CASU) Even though we have used a well-tested, to be still ongoing, as suggested by the pipeline1. We estimate that our survey robust YSO selection method, remain- outflow sources that are clearly seen in should have detected, for a population as ing contamination from extragalactic the north of NGC 2071 and in a chain of young as ~ 2 Myr at a distance of about sources, foreground main-sequence cool young stellar objects to the southwest 400 pc (i.e., the case of Orion B), essen- dwarfs, and background red giants is of NGC 2068. Our VISTA images were tially all objects from ~1 MA down to ~ 5 possible. Using the Galactic stellar popu- obtained through the ZYJHKs filters (0.9– Jupiter masses (MJup) in a region showing lation model by Robin et al. (2003), we find 2.2 μm) and achieved excellent sensitivity, less than 1 mag of visual interstellar that the expected number of background e.g., a 5σ detection limit of Ks ~ 18.5 mag, extinction. giants in the direction of our observed The Messenger 162 – December 2015 43 Astronomical Science Petr-Gotzens M. et al., Young Stellar Objects in the Orion B Cloud area, and within the magnitude limits of M/Mी Figure 3. The Ks-band our survey, is very low (~ 3 stars). Red 3.31.0 0.22 0.05 0.02 0.004 luminosity function (KLF) of the region targeted in background giants generally appear much Orion B before (empty Saturation limitCompleteness limit brighter than young Orion members in the histogram) and after same effective temperature range and (line-filled histogram) are therefore easily distinguishable. Simi- correction for interstellar extinction. The labels on larly, we find from the following experi- 10 the upper x-axis indicate s ment that the number of possible galaxy the corresponding stellar contaminants is very low: we take the mass according to the object VISTA 2-Myr isochrone. SWIRE (Spitzer Wide-area Infrared Extra- of The continuous and galactic) catalogue and select an area the dashed vertical lines same in size as our target area and then indicate the complete- Number place this sample of extragalactic objects 1 ness and the saturation behind the Orion B Molecular Cloud. In limit of the VISTA Ks- band photometry, practice this means applying extinction to respectively. The contin- the extragalactic objects according to uous curve is the KLF of our extinction map of Orion B. Then, we the Trapezium Cluster, apply our YSO multicolour selection crite- scaled to the peak of 81012141618 the Orion B KLF. ria to the reddened SWIRE catalogue Ks magnitude objects and check how many targets would be classified as YSOs. Only three nosities, masses and presence of cir- KLF of Orion B shows a broad peak at objects from the SWIRE catalogue were cumstellar discs. The estimate of the approximately 0.3–0.7 MA before it classified as YSOs (see also lower right YSO masses is probably the most difficult steadily declines into the substellar mass panels of Figure 2). In fact, visual inspec- and we derive it indirectly from the regime. The fraction of substellar objects tion of all 188 YSO candidates revealed YSOs’ luminosity at Ks-band. Particularly compared to the total number of YSOs two objects which appear extended in interesting is the frequency mass distri- is 28 %, which, after a correction for con- the VISTA images and could be clearly bution of the YSOs, i.e., the shape of tamination with field stars, is more like identified as galaxies.
Load more

Recommended publications
  • Multicolor Photometric Behavior of the Young Stellar Object V1704 Cygni
    Multicolor photometric behavior of the young stellar object V1704 Cygni Sunay Ibryamov1, Evgeni Semkov2, Stoyanka Peneva2, U˘gur Karadeniz3 1 Department of Physics and Astronomy, University of Shumen, 115, Universitetska Str., 9700 Shumen, Bulgaria 2 Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72, Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria 3 Department of Physics, Izmir Institute of Technology, Urla, 35430 Izmir, Turkey [email protected] (Submitted on 22.01.2018. Accepted on 20.02.2018) Abstract. Results from BV RI photometric observations of the pre-main sequence star V1704 Cyg collected during the time period from August 2010 to December 2017 are presented. The star is located in the star-forming HII region IC 5070 and it exhibits photometric variability in all optical passbands. After analyzing the obtained data, V1704 Cyg is classified as a classical T Tauri star. Key words: stars: pre-main sequence, stars: variables: T Tauri, star: individual: (V1704 Cyg) 1. Introduction One of the most frequent types of pre-main sequence (PMS) stars are the low-mass (M ≤ 2M⊙) T Tauri stars (TTSs). The first study of the TTSs as a separate class of variables with the prototype star T Tau was made by Joy (1945). These stars show irregular photometric variability and emission spectra. TTSs are divided into two sub-classes: classical T Tauri stars (CTTSs) still actively accreting from their massive circumstellar disks and the weak- line T Tauri stars (WTTSs) without evidence of disk accretion (M´enard
    [Show full text]
  • Young Stellar Object Candidates Toward the Orion Region Selected from GALEX (Research Note)
    A&A 572, A89 (2014) Astronomy DOI: 10.1051/0004-6361/201424629 & c ESO 2014 Astrophysics Young stellar object candidates toward the Orion region selected from GALEX (Research Note) Nestor Sanchez, Ana Inés Gómez de Castro, Fátima Lopez-Martinez, and Javier López-Santiago S. D. Astronomía y Geodesia, Fac. CC. Matemáticas, Universidad Complutense de Madrid, 28040 Madrid, Spain e-mail: [email protected] Received 18 July 2014 / Accepted 28 October 2014 ABSTRACT We analyze 359 ultraviolet tiles from the All Sky Imaging Survey of the space mission GALEX covering roughly 400 square degrees toward the Orion star-forming region. There are a total of 1 555 174 ultraviolet sources that were cross-matched with other catalogs (2MASS, UCAC4, SDSS, DENIS, CMC15, and WISE) to produce a list of 290 717 reliable sources with a wide range of photometric information. Using different color selection criteria, we identify 111 young stellar object candidates showing both ultraviolet and infrared excesses, of which 81 are new identifications. We discuss the spatial distribution, the spectral energy distributions, and other physical properties of these stars. Their properties are, in general, compatible with those expected for T Tauri stars. This population of TTS candidates is widely dispersed around the Orion molecular cloud. Key words. stars: low-mass – stars: pre-main sequence – stars: variables: T Tauri, Herbig Ae/Be – ultraviolet: stars 1. Introduction and magnetic stellar activity (Edwards et al. 1994; Muzerolle et al. 1998). As spectroscopic observations are time consuming The current paradigm for low-mass star formation catego- and are sometimes restricted to bright objects, a good strategy is rizes young stellar objects (YSOs) into four general classes: to perform spectroscopic follow-ups only for the most reliable Class 0 sources are faint central protostars surrounded by a YSO candidates selected using photometric methods.
    [Show full text]
  • Pre-Main-Sequence Star
    Pre-main-sequence star A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of interstellar dust and gas. After the protostar blows away this envelope, it is optically visible, and appears on the stellar birthline in the Hertzsprung-Russell diagram. At this point, the star has acquired nearly all of its mass but has not yet started hydrogen burning (i.e. nuclear fusion of hydrogen). The star then contracts, its internal temperature rising until it begins hydrogen burning on the zero age main sequence. This period of contraction is the pre-main sequence stage.[1][2][3][4] An observed PMS object can either be a T Tauri star, if it has fewer than 2 solar masses (M☉), or else a Herbig Ae/Be star, if it has 2 to 8 M☉. Yet more massive stars have no pre-main-sequence stage because they contract too quickly as protostars. By the time they become visible, the hydrogen in their centers is already fusing and they are main-sequence objects. The energy source of PMS objects is gravitational contraction, as opposed to hydrogen burning in main-sequence stars. In the Hertzsprung–Russell diagram, pre-main-sequence stars with more than 0.5 M☉ first move vertically downward along Hayashi tracks, then leftward and horizontally along Henyey tracks, until they finally halt at the main sequence.
    [Show full text]
  • Selection of Spitzer Young Stellar Object Candidates Using Deep Learning Classifiers
    Selection of Spitzer Young Stellar Object candidates using Deep Learning classifiers David Cornu and Julien Montillaud linkedin page UTINAM, Univ. Bourgogne Franche-Comt´e, Besan¸con,France 1 - Introduction 3 - Deep Learning Observing Young Stellar Objects (YSOs) enables us to characterize the star forming regions, In our case, we rely on one of the most famous and widely used supervised-learning approach e.g. by their star formation efficiency and history or by their density distribution. They are : Artifical Neural Networks (ANN). The neurons in ANN are defined as a mathematical classified into evo lutionary stages (class 0, I, II) using their infrared (IR) Spectral Energy model performing weighted sums of an input vector (which represents different dimensions of Distribution (SED). The Spitzer telescope can be used for such classification using his the same object to classify). It then compares the result to a threshold activation function IRAC bands at 3.6, 4.5, 5.6, 8 µm and MIPS 24 µm, allowing us to distinguish IR excess in and changes the state of the neuron to 1 or 0 (firing or not). The learning process consist in class I or the disk emission of the class II from other kind of objects/contaminents. comparing the expected value (target) with the result obtained by the activation of the neuron, and then modify the weights according to the error gradient, hence learning anti/correlations. m XX h = Xi!i i=1 ( 1 if h > θ O = g(h) = 0 if h ≤ θ Performing complex classification requires more than one neuron. We can add them in one layer, fully connecting each neuron to all the inputs, and we can add multiple layers by making some neurons take the output of the previous layer as their own inputs.
    [Show full text]
  • THE STAR FORMATION NEWSLETTER an Electronic Publication Dedicated to Early Stellar Evolution and Molecular Clouds
    THE STAR FORMATION NEWSLETTER An electronic publication dedicated to early stellar evolution and molecular clouds No. 148 — 15 February 2005 Editor: Bo Reipurth ([email protected]) Abstracts of recently accepted papers The Brightest OH Maser in the Sky? A Flare of Emission in W75 N A. V. Alakoz1, V. I. Slysh1, M. V. Popov1, and I. E. Val’tts1 1 Astro Space Center of the Lebedev Physical Institute of RAS, Profsoyuznaya Str. 84/32, Moscow 117997, Russia E-mail contact: [email protected] A flare of maser radio emission in the OH-line 1665 MHz has been discovered in the star forming region W75 N in 2003, with the flux density about 1000 Jy. At the moment of observations this was the strongest OH maser detected during the whole history of studies since the discovery of cosmic masers in 1965. The flare emission is linearly polarized with a degree of polarization near 100%. A weaker flare with a flux of 145 Jy was observed in this source in 2000 – 2001, which was probably a precursor of the powerful flare. Intensity of two other spectral features has decreased after beginning of the flare. Such variation of the intensity of maser condensation emission (increasing of one and decreasing of other) can be explained by passing of the magneto hydrodynamic shock across the regions of the enhanced gas concentration. Accepted by Astronomy Letters astro-ph/0501539 (2005) Pushing the Envelope: The Impact of an Outflow at the Earliest Stages of Star Forma- tion H´ector G. Arce1 and Anneila I.
    [Show full text]
  • First Firm Spectral Classification of an Early-B Pre-Main-Sequence Star: B275 in M
    A&A 536, L1 (2011) Astronomy DOI: 10.1051/0004-6361/201118089 & c ESO 2011 Astrophysics Letter to the Editor First firm spectral classification of an early-B pre-main-sequence star: B275 in M 17 B. B. Ochsendorf1, L. E. Ellerbroek1, R. Chini2,3,O.E.Hartoog1,V.Hoffmeister2,L.B.F.M.Waters4,1, and L. Kaper1 1 Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, PO Box 94249, 1090 GE Amsterdam, The Netherlands e-mail: [email protected]; [email protected] 2 Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany 3 Instituto de Astronomía, Universidad Católica del Norte, Antofagasta, Chile 4 SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands Received 14 September 2011 / Accepted 25 October 2011 ABSTRACT The optical to near-infrared (300−2500 nm) spectrum of the candidate massive young stellar object (YSO) B275, embedded in the star-forming region M 17, has been observed with X-shooter on the ESO Very Large Telescope. The spectrum includes both photospheric absorption lines and emission features (H and Ca ii triplet emission lines, 1st and 2nd overtone CO bandhead emission), as well as an infrared excess indicating the presence of a (flaring) circumstellar disk. The strongest emission lines are double-peaked with a peak separation ranging between 70 and 105 km s−1, and they provide information on the physical structure of the disk. The underlying photospheric spectrum is classified as B6−B7, which is significantly cooler than a previous estimate based on modeling of the spectral energy distribution. This discrepancy is solved by allowing for a larger stellar radius (i.e.
    [Show full text]
  • HST/NICMOS Observations of a Proto-Brown Dwarf Candidate The
    A&A 433, L33–L36 (2005) Astronomy DOI: 10.1051/0004-6361:200500098 & c ESO 2005 Astrophysics Editor HST/NICMOS observations of a proto-brown dwarf candidate the 1,2,3 1,4,5 1 6 1 1 to D. Apai ,L.V.Tóth , T. Henning ,R.Vavrek ,Z.Kovács ,andD.Lemke 1 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany e-mail: [email protected] 2 Steward Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA Letter 3 NASA Astrobiology Institute 4 Department of Astronomy of the Loránd Eötvös University, Pázmány Péter sétány 1, 1117 Budapest, Hungary 5 Konkoly Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary 6 Astrophysics Missions Division, ESTEC, Keplerlann 1, Norwijk 2201, The Netherlands Received 6 December 2004 / Accepted 18 February 2005 Abstract. We present deep HST/NICMOS observations peering through the outflow cavity of the protostellar candidate IRAS 04381+2540 in the Taurus Molecular Cloud-1. A young stellar object as central source, a jet and a very faint and close (0.6) companion are identified. The primary and the companion have similar colours, consistent with strong reddening. We argue that the companion is neither a shock-excited knot nor a background star. The colour/magnitude information predicts a substellar upper mass limit for the companion, but the final confirmation will require spectroscopic information. Because of its geometry, young age and its rare low-mass companion, this system is likely to provide a unique insight into the formation of brown dwarfs. Key words.
    [Show full text]
  • The Agb Newsletter
    THE AGB NEWSLETTER An electronic publication dedicated to Asymptotic Giant Branch stars and related phenomena Official publication of the IAU Working Group on Abundances in Red Giants No. 240 — 1 July 2017 http://www.astro.keele.ac.uk/AGBnews Editors: Jacco van Loon, Ambra Nanni and Albert Zijlstra Figure 1: The planetary nebula Kronberger 24 in Hα and [O iii]. It is round! Thanks to Sakib Rasool for suggesting. See http://www.cxielo.ch/gallery/f/kn24 for more details. 1 Editorial Dear Colleagues, It is a pleasure to present you the 240th issue of the AGB Newsletter. Please consider John Lattanzio’s 60th birthday party – something not to be missed! Note also the possible opportunity to join a large programme with the James Clerk Maxwell Telescope. The next issue is planned to be distributed sometime in August – African animals willing. Editorially Yours, Jacco van Loon, Ambra Nanni and Albert Zijlstra Food for Thought This month’s thought-provoking statement is: Stars grow when they lose (mass) Reactions to this statement or suggestions for next month’s statement can be e-mailed to [email protected] (please state whether you wish to remain anonymous) 2 Refereed Journal Papers A SOFIA FORCAST grism study of the mineralogy of dust in the winds of proto-planetary nebulæ: RVTauri stars and SRd variables R.A. Arneson1, R.D. Gehrz1, C.E. Woodward1, L.A. Helton2, D. Shenoy1, A. Evans3, L.D.Keller4, K.H. Hinkle5, M. Jura6, T. Lebzelter7, C.M. Lisse8, M.T. Rushton9 and J. Mizrachi10 1Minnesota Institute for Astrophysics, USA 2USRA–SOFIA
    [Show full text]
  • The T Tauri Star RY Tauri As a Case Study of the Inner Regions of Circumstellar Dust Disks
    A&A 478, 779–793 (2008) Astronomy DOI: 10.1051/0004-6361:20077049 & c ESO 2008 Astrophysics The T Tauri star RY Tauri as a case study of the inner regions of circumstellar dust disks A. A. Schegerer1,S.Wolf1, Th. Ratzka2, and Ch. Leinert1 1 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: [email protected] 2 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany Received 3 January 2007 / Accepted 13 November 2007 ABSTRACT Aims. We study the inner region (∼1.0 AU up to a few 10 AUs) of the circumstellar disk around the “classical” T Tauri star RY Tau. Our aim is to find a physical description satisfying the available interferometric data, obtained with the mid-infrared interferometric instrument at the Very Large Telescope Interferometer, as well as the spectral energy distribution in the visible to millimeter wave- length range. We also compare the findings with the results of similar studies, including those of intermediate-mass Herbig Ae/Be stars. Methods. Our analysis is done within the framework of a passively heated circumstellar disk, which is optionally supplemented by the effects of accretion and an added envelope. To achieve a more consistent and realistic model, we used our continuum transfer code MC3D. In addition, we studied the shape of the 10 µm silicate emission feature in terms of the underlying dust population, both for single-dish and for interferometric measurements. Results. We show that a modestly flaring disk model with accretion can explain both the observed spectral energy distribution and the mid-infrared visibilities obtained with the mid-infrared infrared instrument.
    [Show full text]
  • Star Formation in the Galaxy, an Observational Overview
    1 Star Formation in the Galaxy, An Observational Overview Charles J. Lada1;¤) 1Harvard-Smithsonian Center for Astrophysics, Cambridge, MA USA 02138 (Received ) The problems of star and planet formation are among the most important challenges facing modern astrophysical research. Stars and their accompanying planetary systems are continuously being formed in the Galaxy enabling direct observation and investigation of the star forming process. However, stars form invisibly deep within cold and dark molecular clouds. Observations of these stellar birth sites at infrared and millimeter wavelengths from space and the ground have resulted in considerable progress toward a physical understanding of stellar origins. In this contribution I will review the empirical basis for our current understanding of the process of star formation with an emphasis on the origin of low mass (sunlike) stars. x1. Introduction Stars are the fundamental objects of the Cosmos. They are the homes of plane- tary systems and they provide the energy necessary for the development and main- tenance of life. The evolution of stars drives the evolution of all stellar systems in- cluding clusters and galaxies. Stellar Evolution also controls the chemical evolution of the universe. The physical natures and life histories of stars are well described by the theory of stellar structure and evolution, one of the great achievements of 20th century astronomy. According to this theory stars are self-gravitating balls of (mostly) hydrogen gas that act as thermonuclear furnaces to convert the primary product of the big bang (hydrogen) into the heavier elements of the periodic table. For most of its life a star maintains a state of stable equilibrium in which the in- ward force of gravity is balanced by the outward force of pressure.
    [Show full text]
  • A Post Asymptotic Giant Branch Or a Young Stellar Object Variable?
    "Peremennye Zvezdy", Prilozhenie, vol. 8, N 39 (2008) OGLE II Sco_SC1 72677: A Post Asymptotic Giant Branch or a Young Stellar Object Variable? J. Greaves Northants, England , UK Received: 8.08.2008; accepted: 10.11.2008 (E-mail for contact: [email protected]) Star Name: OGLE II Sco_SC1 72677 Coordinates (J2000): 16 40 24.88, -44 24 53.2 Variability type: RCB:/IA:; Limits, System: 13.5-14.7 (I); Period: Epoch: JD Remarks: OGLE II Sco_SC1 72677 has a lightcurve (Szymanski 2005, Udalski et al. 1997) somewhat reminiscent of stars of type RCB, with a slow recovery from fading at the beginning of the data and the suggestion of a moderately rapid decline in brightness towards the end of the data. However, the recovery phase is somewhat rapid compared to a typical RCB star, and the seasonal gaps hide whether faint events occurred at those times. The spectral energy distribution (SED) in the near infrared from 2MASS, MSX6C and IRAS data does not support a post Asymptotic Giant Branch star (post AGB), however, as can be seen from examining the SEDs of known post AGBs (e.g. Szczerba et al. 2007; http://www.ncac.torun.pl/postagb) where usually the flux at 60 and 100 microns shows a distinct downturn. Models and SED fits for Young Stellar Objects (YSOs) (Robitaille et al. 2007; http://caravan.astro.wisc.edu/protostars/) better fit the situation, with the extended envelopes of stage one YSOs usually leading to higher fluxes at the longer IRAS wavelengths. This would make the star one of a class of Herbig Ae/Be stars known to sometimes undergo obscuration events.
    [Show full text]
  • Pre-Main-Sequence Stars in the Young Open Cluster NGC 1893 II
    A&A 471, 485–497 (2007) Astronomy DOI: 10.1051/0004-6361:20066654 & c ESO 2007 Astrophysics Pre-main-sequence stars in the young open cluster NGC 1893 II. Evidence for triggered massive star formation I. Negueruela1,2,3,A.Marco1,3, G. L. Israel4, and G. Bernabeu1 1 Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain e-mail: [email protected] 2 Observatoire de Strasbourg, 11 rue de l’Université, 67000 Strasbourg, France 3 Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK 4 Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone, Italy Received 27 October 2006 / Accepted 27 March 2007 ABSTRACT Context. The open cluster NGC 1893 illuminating the H ii region IC 410 contains a moderately large population of O-type stars and is one of the youngest clusters observable in the optical range. It is suspected of harbouring a large population of pre-main-sequence (PMS) stars. Aims. We have probed the stellar population of NGC 1893 in an attempt to determine its size and extent. In particular, we look for signs of sequential star formation. Methods. We classify a large sample of cluster members with new intermediate-resolution spectroscopy. We used Hα slitless spec- troscopy of the field to search for emission-line objects, identifying 18 emission-line PMS stars. We then combined existing optical photometry with the 2MASS JHKS photometry to detect stars with infrared excesses, finding close to 20 more PMS candidates. Results.
    [Show full text]