scholarly journals Unveiling the massive stars in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 230-234 ◽  
Author(s):  
H. Dong ◽  
J. Mauerhan ◽  
M. R. Morris ◽  
Q. D. Wang ◽  
A. Cotera
Keyword(s):  
Massive Star ◽  
Galactic Center ◽  
Massive Stars ◽  
Star Clusters ◽  
Radial Velocities ◽  
Stellar Winds ◽  
Band Spectra

AbstractWe present our recent efforts to unveil and understand the origin of massive stars outside the three massive star clusters in the Galactic center. From our Hubble/NICMOS survey of the Galactic center, we have identified 180 Paschen-α emitting sources, most of which should be evolved massive stars with strong optically thin stellar winds. Recently, we obtained Gemini GNIRS/NIFS H- and K-band spectra of eight massive stars near the Arches cluster. From their radial velocities, ages and masses, we suggest that in our sample, two stars are previous members of the Arches cluster, while other two stars embedded in the H1/H2 Hii regions formed in-situ.

scholarly journals Massive stars in the young cluster VVV CL074

2019 ◽  
Vol 627 ◽  
pp. A170 ◽  
Author(s):  
F. Martins ◽  
A.-N. Chené ◽  
J.-C. Bouret ◽  
J. Borissova ◽  
J. Groh ◽  
...  
Keyword(s):  
Massive Star ◽  
Galactic Center ◽  
Massive Stars ◽  
Stellar Content ◽  
Integral Field Spectroscopy ◽  
The Galaxy ◽  
Infrared Spectral ◽  
Band Spectra ◽  
Stellar Properties ◽  
Massive Clusters

Context. The evolution of massive stars is not fully constrained. Studies of young massive clusters hosting various populations of massive stars can help refine our understanding of the life and fate of massive stars. Aims. In this context, our goal is to study the massive stellar content of the young massive cluster VVV CL074. Methods. We obtained K-band spectroscopy of the brightest cluster members in order to identify the massive star population. We also determined the stellar properties of the cluster’s massive stars to better quantify the evolutionary sequences linking different types of massive stars. We collected integral field spectroscopy of selected fields in the cluster VVV CL074 with SINFONI on the ESO/VLT. We performed a spectral classification based on the K-band spectra and comparison to infrared spectral atlases. We determined the stellar parameters of the massive stars from analysis with atmosphere models computed with the code CMFGEN. Results. We uncover a population of 25 early-type (OB and Wolf–Rayet) stars, 19 being newly discovered by our observations out of which 15 are likely cluster members. The cluster’s spectrophotometric distance is 10.2 ± 1.6 kpc, placing it close to the intersection of the galactic bar and the Norma arm, beyond the galactic center. This makes VVV CL074 one the farthest young massive clusters identified so far. Among the massive stars population, three objects are Wolf–Rayet stars, the remaining are O and B stars. From the Hertzsprung–Russell diagram we find that most stars have an age between 3 and 6 Myr according to the Geneva evolutionary tracks. WN8 and WC8-9 stars are the descendants of stars with initial masses between 40 and 60 M⊙. The massive star population of VVV CL074 is very similar to that of the cluster DBS2003-179 and to a lesser extent to that of the Quintuplet cluster, indicating the same age. The central cluster of the Galaxy is ∼3 Myr older. From the comparison of the massive stars populations in these four clusters, one concludes that galactic stars with an initial mass in the range 40–60 M⊙ likely go through a WN8-9 phase.

scholarly journals The influence of feedback from massive stars on the formation and emergence of massive clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 177-183
Author(s):  
James E. Dale
Keyword(s):  
Large Scale ◽  
Massive Star ◽  
Massive Stars ◽  
Cluster Structure ◽  
Star Clusters ◽  
Stellar Feedback ◽  
Making Sense ◽  
Formation Efficiency ◽  
Massive Clusters ◽  
Made In

AbstractMassive star clusters are of fundamental importance both observationally, since they are visible at such great distances, and theoretically, because of their influence on the large–scale ISM. Understanding stellar feedback is a prerequisite for making sense of their formation and early evolution, since feedback influences cluster structure, star formation efficiency, and sets the timescales on which clusters emerge from their parent clouds to become optically visible. I review the progress made in understanding these issues from a numerical perspective.

scholarly journals Metallicity studies of the Galactic center: evidence for a top-heavy star formation history?

2013 ◽  
Vol 9 (S303) ◽  
pp. 252-253
Author(s):  
Francisco Najarro ◽  
Diego de la Fuente ◽  
Tom R. Geballe ◽  
Don F. Figer
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Local Group ◽  
Galactic Center ◽  
Massive Stars ◽  
Star Formation History ◽  
Test Bed ◽  
Formation History ◽  
History Of ◽  
Stellar Properties

AbstractThe Galactic center (GC) region hosts three of the most massive resolved young clusters in the Local Group and constitutes a test bed for studying the star formation history of the region and inferring the possibility of a top-heavy scenario. Further, recent detection of a large number of apparently isolated massive stars within the inner 80 pc of the Galactic center has raised fundamental questions regarding massive star formation in a such a dense and harsh environment. Noting that most of the isolated massive stars have spectral analogs in the Quintuplet cluster, we have undertaken a combined analysis of the infrared spectra of both selected Quintuplet stars and the isolated objects using Gemini spectroscopy. We present preliminary results, aiming at α-elements versus iron abundances, stellar properties, ages and radial velocities which will differentiate the top-heavy and star-formation scenarios.

scholarly journals Stellar population of the superbubble N 206 in the LMC

2018 ◽  
Vol 615 ◽  
pp. A40 ◽  
Author(s):  
V. Ramachandran ◽  
W.-R. Hamann ◽  
R. Hainich ◽  
L. M. Oskinova ◽  
T. Shenar ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Mechanical Energy ◽  
Star Formation History ◽  
Photon Flux ◽  
Stellar Winds ◽  
Spectral Analyses ◽  
Ob Stars ◽  
Hot Gas

Context. Clusters or associations of early-type stars are often associated with a “superbubble” of hot gas. The formation of such superbubbles is caused by the feedback from massive stars. The complex N 206 in the Large Magellanic Cloud (LMC) exhibits a superbubble and a rich massive star population. Aims. Our goal is to perform quantitative spectral analyses of all massive stars associated with the N 206 superbubble in order to determine their stellar and wind parameters. We compare the superbubble energy budget to the stellar energy input and discuss the star formation history of the region. Methods. We observed the massive stars in the N 206 complex using the multi-object spectrograph FLAMES at ESO’s Very Large Telescope (VLT). Available ultra-violet (UV) spectra from archives are also used. The spectral analysis is performed with Potsdam Wolf–Rayet (PoWR) model atmospheres by reproducing the observations with the synthetic spectra. Results. We present the stellar and wind parameters of the OB stars and the two Wolf–Rayet (WR) binaries in the N 206 complex. Twelve percent of the sample show Oe/Be type emission lines, although most of them appear to rotate far below critical. We found eight runaway stars based on their radial velocity. The wind-momentum luminosity relation of our OB sample is consistent with the expectations. The Hertzsprung–Russell diagram (HRD) of the OB stars reveals a large age spread (1–30 Myr), suggesting different episodes of star formation in the complex. The youngest stars are concentrated in the inner part of the complex, while the older OB stars are scattered over outer regions. We derived the present day mass function for the entire N 206 complex as well as for the cluster NGC 2018. The total ionizing photon flux produced by all massive stars in the N 206 complex is Q0 ≈ 5 × 1050 s−1, and the mechanical luminosity of their stellar winds amounts to Lmec = 1.7 × 1038 erg s−1. Three very massive Of stars are found to dominate the feedback among 164 OB stars in the sample. The two WR winds alone release about as much mechanical luminosity as the whole OB star sample. The cumulative mechanical feedback from all massive stellar winds is comparable to the combined mechanical energy of the supernova explosions that likely occurred in the complex. Accounting also for the WR wind and supernovae, the mechanical input over the last five Myr is ≈ 2.3 × 1052 erg. Conclusions. The N206 complex in the LMC has undergone star formation episodes since more than 30 Myr ago. From the spectral analyses of its massive star population, we derive a current star formation rate of 2.2 × 10−3 M⊙ yr−1. From the combined input of mechanical energy from all stellar winds, only a minor fraction is emitted in the form of X-rays. The corresponding input accumulated over a long time also exceeds the current energy content of the complex by more than a factor of five. The morphology of the complex suggests a leakage of hot gas from the superbubble.

scholarly journals On the early evolution of massive star clusters: the case of cloud D1 and its embedded cluster in NGC 5253

2020 ◽  
Vol 494 (1) ◽  
pp. 97-107 ◽  
Author(s):  
Sergiy Silich ◽  
Guillermo Tenorio-Tagle ◽  
Sergio Martínez-González ◽  
Jean Turner
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Star Clusters ◽  
Early Evolution ◽  
Mass Loading ◽  
Low Mass Stars ◽  
Stellar Cluster ◽  
Star Forming ◽  
Cluster Phase ◽  
Protostellar Discs

ABSTRACT We discuss a theoretical model for the early evolution of massive star clusters and confront it with the ALMA, radio, and infrared observations of the young stellar cluster highly obscured by the molecular cloud D1 in the nearby dwarf spheroidal galaxy NGC 5253. We show that a large turbulent pressure in the central zones of D1 cluster may cause individual wind-blown bubbles to reach pressure confinement before encountering their neighbours. In this case, stellar winds energy is added to the hot shocked wind pockets of gas around individual massive stars that leads them to meet and produce a cluster wind in time-scales less than 105 yr. In order to inhibit the possibility of cloud dispersal, or the early negative star formation feedback, one should account for mass loading that may come, for example, from pre-main-sequence (PMS) low-mass stars through photoevaporation of their protostellar discs. Mass loading at a rate in excess of 8 × 10−9 M⊙ yr−1 per each PMS star is required to extend the hidden star cluster phase in this particular cluster. In this regime, the parental cloud remains relatively unperturbed, while pockets of molecular, photoionized and hot gas coexist within the star-forming region. Nevertheless, the most likely scenario for cloud D1 and its embedded cluster is that the hot shocked winds around individual massive stars should merge at an age of a few million of years when the PMS star protostellar discs vanish and mass loading ceases that allows a cluster to form a global wind.

scholarly journals Massive Stars in the Galactic Center

2007 ◽  
Vol 3 (S250) ◽  
pp. 257-264
Author(s):  
F. Martins ◽  
D. J. Hillier ◽  
R. Genzel ◽  
F. Eisenhauer ◽  
T. Ott ◽  
...  
Keyword(s):  
Massive Star ◽  
Near Infrared ◽  
Galactic Center ◽  
Massive Stars ◽  
Evolutionary Status ◽  
Infrared Spectral Range ◽  
Different Types ◽  
Infrared Spectral ◽  
Observational Techniques ◽  
Massive Clusters

AbstractWe present results of two studies aiming at better understanding the properties of massive stars in the Galactic Center. We focus on the youngest and oldest of the three massive clusters harboring this region, namely the Arches and central cluster. We show that the development of powerful observational techniques in the near infrared spectral range (mainly 3D spectroscopy) allows to uncover the entire massive star population in these clusters. Using CMFGEN models, we derive the classical stellar and wind properties of 46 stars, as well as their surface abundances. The latter allow us to investigate in detail their evolutionary status and to identify evolutionary sequences between different types of stars. We thus constrain stellar evolution in the upper part of the HR diagram.

scholarly journals X-ray diagnostics of massive star winds

2016 ◽  
Vol 12 (S329) ◽  
pp. 151-155
Author(s):  
L. M. Oskinova ◽  
R. Ignace ◽  
D. P. Huenemoerder
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
Massive Star ◽  
Massive Stars ◽  
Stellar Winds ◽  
X Rays ◽  
Early Type ◽  
Stellar Rotation ◽  
X Ray ◽  
Early Type Stars

AbstractObservations with powerful X-ray telescopes, such as XMM-Newton and Chandra, significantly advance our understanding of massive stars. Nearly all early-type stars are X-ray sources. Studies of their X-ray emission provide important diagnostics of stellar winds. High-resolution X-ray spectra of O-type stars are well explained when stellar wind clumping is taking into account, providing further support to a modern picture of stellar winds as non-stationary, inhomogeneous outflows. X-ray variability is detected from such winds, on time scales likely associated with stellar rotation. High-resolution X-ray spectroscopy indicates that the winds of late O-type stars are predominantly in a hot phase. Consequently, X-rays provide the best observational window to study these winds. X-ray spectroscopy of evolved, Wolf-Rayet type, stars allows to probe their powerful metal enhanced winds, while the mechanisms responsible for the X-ray emission of these stars are not yet understood.

scholarly journals Self-shielding clumps in starburst clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 251-252
Author(s):  
Jan Palouš ◽  
Richard Wünsch ◽  
Soňa Ehlerová ◽  
Guillermo Tenorio-Tagle
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Critical Mass ◽  
Free Fall ◽  
Circumstellar Disks ◽  
Cluster Center ◽  
Stellar Winds ◽  
Heating Efficiency ◽  
Temperature And Pressure ◽  
Mass Form

AbstractYoung and massive star clusters above a critical mass form thermally unstable clumps reducing locally the temperature and pressure of the hot 107 K cluster wind. The matter reinserted by stars, and mass loaded in interactions with pristine gas and from evaporating circumstellar disks, accumulate on clumps that are ionized with photons produced by massive stars. We discuss if they may become self-shielded when they reach the central part of the cluster, or even before it, during their free fall to the cluster center. Here we explore the importance of heating efficiency of stellar winds.

scholarly journals Massive Star Formation in the Sparsest Environments

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Sally Oey ◽  
Joel B. Lamb
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Hii Regions ◽  
Magellanic Cloud ◽  
Small Magellanic Cloud ◽  
Massive Star Formation ◽  
Ob Stars ◽  
Runaway Stars

AbstractThere is growing evidence that massive stars sometimes form in extremely sparse environments. The RIOTS4 survey presents a variety of evidence supporting this scenario, including a sample of 14 OB stars in the Small Magellanic Cloud (SMC) that appear to have formed in situ as field stars. This is based on the presence of dense, symmetric HII regions hosting apparent non-runaway stars. We also present a spatially complete IMF of SMC field OB stars for masses > 7 M⊙, showing that the slope is much steeper than the Salpeter value. The binary fraction among field OB stars is also the same as in clusters, based on a RIOTS4 subsample. These results suggest a relative, but incomplete, suppression of massive star formation in the sparsest regimes.

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