A Spectral Atlas of Hot, Luminous Stars at 2 Microns

Hanson, M. M.; Conti, Peter S.; Rieke, M. J.

doi:10.1086/192366

Cited by 320 publications

(583 citation statements)

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“…Kleinmann and Hall (1986) provide a 2.0 -2.5 µm spectral atlas of late-type stars that demonstrates that if S0-2 is a K5 giant star, then it should have deep CO absorption lines, which definitively were not detected in either this experiment or our earlier experiment reported by Gezari et al (2002). In contrast, the spectral atlas of 180 O and B stars constructed by Hanson, Conti and Rieke (1996) shows that an O9 main sequence star both lacks the CO absorption and has Br γ and He I (2.1126 µm) consistent with the observed values. Furthermore, stars earlier than O8 in this comparison sample show NIII (2.115 µm) in emission and He II (2.1885 µm) in absorption above our 3 σ thresholds; the lack of photospheric He I (2.058 µm) absorption does not provide any additional constraints.…”

Section: Stellar Astrophysicsmentioning

confidence: 58%

Full Three Dimensional Orbits For Multiple Stars on Close Approaches to the Central Supermassive Black Hole

et al. 2003

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With the advent of adaptive optics on the W. M. Keck 10m telescope, two significant steps forward have been taken in building the case for a supermassive black hole at the center of the Milky Way and understanding the black hole's effect on its environment. Using adaptive optics and speckle imaging to study the motions of stars in the plane of sky with ±∼2 mas precision over the past 7 years, we have obtained the first simultaneous orbital solution for multiple stars. Among the included stars, three are newly identified (S0-16, S0-19, S0-20). The most dramatic orbit is that of the newly identified star S0-16, which passed a mere 60 AU from the central dark mass at a velocity of 9,000 km/s in 1999. The orbital analysis results in a new central dark mass estimate of 3.6(±0.4) × 10 6 (( Ro 8kpc ) 3 M . This dramatically strengthens the case for a black hole at the center of our Galaxy, by confining the dark matter to within a radius of 0.0003 pc or 1,000 R sh and thereby increasing the inferred dark mass density by four orders of magnitude compared to earlier estimates.With the introduction of an adaptive-optics-fed spectrometer, we have obtained the first detection of spectral absorption lines in one of the high-velocity stars, S0-2, one month after its closest approach to the Galaxy's central supermassive black hole. Both Br γ (2.1661 µm) and He I (2.1126 µm) are seen in absorption with equivalent widths and an inferred stellar rotational velocity that are consistent with that of an O8-B0 dwarf, which suggests that S0-2 is a massive (∼15 M ), young (<10 Myr) main sequence star. Similarly, the lack of CO detected in our first AO spectra suggest that several other of the high-velocity stars are also young. This presents a major challenge to star formation theories, given the strong tidal forces that prevail over all distances reached by these stars in their current orbits and the difficulty in migrating these stars inward during their lifetime from further out where tidal forces should no longer preclude star formation.

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Section: Stellar Astrophysicsmentioning

confidence: 58%

Full Three Dimensional Orbits For Multiple Stars on Close Approaches to the Central Supermassive Black Hole

et al. 2003

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“…The spectra of the newly identified O/B stars with S /N > ∼ 50 contain a He I absorption line at 2.113 μm. Hanson et al (1996) showed that this line disappears in early O stars. Therefore the stars with 2.113 μm absorption are later than O7 V, O7 III, or O9 I.…”

Section: O/b Star Mass Estimatesmentioning

confidence: 97%

KMOS view of the Galactic centre

Feldmeier-Krause

Neumayer

Schödel

et al. 2015

A&A

106

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Context. The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4 pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also > ∼ 100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3−8 Myr old. Aims. Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5 pc of the Galactic centre. The distribution and kinematics of earlytype stars are essential to understand the formation and growth of the nuclear star cluster. Methods. We cover the central >4 pc 2 (0.75 sq. arcmin) of the Galactic centre using the integral-field spectrograph KMOS (VLT). We extracted more than 1000 spectra from individual stars and identified early-type stars based on their spectra. Results. Our data set contains 114 bright early-type stars: 6 have narrow emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and 76 are O/B type stars. Our wide-field spectroscopic data confirm that the distribution of young stars is compact, with 90% of the young stars identified within 0.5 pc of the nucleus. We identify 24 new O/B stars primarily at large radii. We estimate photometric masses of the O/B stars and show that the total mass in the young population is > ∼ 12 000 M . The O/B stars all appear to be bound to the Milky Way nuclear star cluster, while less than 30% belong to the clockwise rotating disk. We add one new star to the sample of stars affiliated with this disk. Conclusions. The central concentration of the early-type stars is a strong argument that they have formed in situ. An alternative scenario, in which the stars formed outside the Galactic centre in a cluster that migrated to the centre, is refuted. A large part of the young O/B stars is not on the disk, which either means that the early-type stars did not all form on the same disk or that the disk is dissolving rapidly.

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“…We estimate a spectral type using the classification scheme from Hanson et al (1996Hanson et al ( , 1998 for the K-and H-band spectra, respectively. An EW of ∼2 Å is measured for the Br-11 absorption line (1.6814 μm).…”

Section: K-bandmentioning

confidence: 99%

Sequential star formation in IRAS 06084-0611 (GGD 12-15)

Maaskant

Bik

Waters

et al. 2011

A&A

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Context. The formation and early evolution of high-and intermediate-mass stars towards the main sequence involves the interplay of stars in a clustered and highly complex environment. To obtain a full census of this interaction, the Formation and Early evolution of Massive Stars (FEMS) collaboration studies a well-selected sample of 10 high-mass star-forming regions. Aims. In this study we examine the stellar content of the high-mass star-forming region centered on IRAS 06084-0611 in the Monoceros R2 cloud. Methods. Using the near-infrared H-and K-band spectra from the VLT/SINFONI instrument on the ESO Very Large Telescope (VLT) and photometric near-infrared NTT/SOFI, 2MASS and Spitzer/IRAC data, we were able to determine the spectral types for the most luminous stars in the cluster. Results. Two very young and reddened massive stars have been detected by SINFONI: a massive young stellar object (YSO) consistent with an early-B spectral type and a Herbig Be star. Furthermore, stars of spectral type G and K are detected while still in the Pre-Main Sequence (PMS) phase. We derive additional properties such as temperatures, extinctions, radii and masses. We present a Hertzsprung-Russell diagram and find most objects having intermediate masses between ∼1.5-2.5 M . For these stars we derive a median cluster age of ∼4 Myr. Conclusions. Using Spitzer/IRAC data we confirm earlier studies that the younger class 0/I objects are centrally located while the class II objects are spread out over a larger area, with rough scale size radii of ∼0.5 pc and ∼1.25 pc respectively. Moreover, the presence of a massive YSO, an ultracompact H ii region and highly reddened objects in the center of the cluster suggest a much younger age of <1 Myr. A possible scenario for this observation would be sequential star formation along the line of sight; from a cluster of intermediate-mass to high-mass stars.

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A Spectral Atlas of Hot, Luminous Stars at 2 Microns

Cited by 320 publications

References 0 publications

Full Three Dimensional Orbits For Multiple Stars on Close Approaches to the Central Supermassive Black Hole

Full Three Dimensional Orbits For Multiple Stars on Close Approaches to the Central Supermassive Black Hole

KMOS view of the Galactic centre

Sequential star formation in IRAS 06084-0611 (GGD 12-15)

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