The Luminosity of the Central Parsec of the Galaxy

The luminosity of the central 5 pc of the Galaxy -encompassing the inner regions of the rotating ring of dust and gas which surrounds the galactic center - emerges primarily at infrared wavelengths in the form of thermal emission from heated dust. The nature and location of the sources which heat the dust can be inferred from the spatial and temperature distribution of the thermal infrared emission (λ>20um), from studies of the ionized gas in this region, and from direct imaging in the near infrared. These observations show that the principal heating sources within this 5-pc region are concentrated within the central parsec of the Galaxy and indicate that the luminosity of these sources is within a factor of two of 107 LO. The near-infrared observations of the compact sources at the galactic center do not reveal a single dominant source but suggest instead that the several components of the IRS-16 complex, taken together, may contribute the bulk of the luminosity; however, the data also permit a single object to dominate the energetics of this region. We draw attention to the striking morphological similarities between the galactic center and the innermost regions of the 30 Doradus nebula in the Large Magellanic Cloud and speculate that the luminosity sources in the galactic center may resemble the early-type supergiants in 30 Doradus.

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High-contrast and resolution near-infrared photometry of the core of R136

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab388 ◽

2021 ◽

Vol 503 (1) ◽

pp. 292-311

Author(s):

Zeinab Khorrami ◽

Maud Langlois ◽

Paul C Clark ◽

Farrokh Vakili ◽

Anne S M Buckner ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Outer Region ◽

Mass Range ◽

Mass Function ◽

Large Magellanic Cloud ◽

Star Forming ◽

The Core ◽

Very Large Telescope ◽

30 Doradus

ABSTRACT We present the sharpest and deepest near-infrared photometric analysis of the core of R136, a newly formed massive star cluster at the centre of the 30 Doradus star-forming region in the Large Magellanic Cloud. We used the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode for the second time with longer exposure time in the H and K filters. Our aim was to (i) increase the number of resolved sources in the core of R136, and (ii) to compare with the first epoch to classify the properties of the detected common sources between the two epochs. Within the field of view (FOV) of 10.8″ × 12.1″ ($2.7\,\text {pc}\times 3.0\, \text {pc}$), we detected 1499 sources in both H and K filters, for which 76 per cent of these sources have visual companions closer than 0.2″. The larger number of detected sources enabled us to better sample the mass function (MF). The MF slopes are estimated at ages of 1, 1.5, and 2 Myr, at different radii, and for different mass ranges. The MF slopes for the mass range of 10–300 M⊙ are about 0.3 dex steeper than the mass range of 3–300 M⊙, for the whole FOV and different radii. Comparing the JHK colours of 790 sources common in between the two epochs, 67 per cent of detected sources in the outer region (r > 3″) are not consistent with evolutionary models at 1–2 Myr and with extinctions similar to the average cluster value, suggesting an origin from ongoing star formation within 30 Doradus, unrelated to R136.

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The Stellar Content of 30 Doradus

Symposium - International Astronomical Union ◽

10.1017/s0074180900040328 ◽

1984 ◽

Vol 108 ◽

pp. 243-253

Author(s):

Nolan R. Walborn

Keyword(s):

Large Magellanic Cloud ◽

Stellar Content ◽

Multiple Systems ◽

Central Cluster ◽

Distant Galaxies ◽

Good Accord ◽

The Galaxy ◽

Spectroscopic Information ◽

H Ii Region ◽

30 Doradus

The supergiant H II region 30 Doradus is placed in context as the optically most spectacular component in a much larger region of recent and current star formation in the Large Magellanic Cloud, as shown by deep Hα photographs and the new IRAS results. The current state of knowledge concerning the concentrated central cluster in 30 Dor is summarized. Spectroscopic information exists for only 24 of the brightest members, most of which are WR stars; however, photometry shows over 100 probable members earlier than BO. The spectral classification of these stars is a difficult observational problem currently being addressed; in the meantime their hypothetical ionizing luminosity is calculated from the photometry and compared with that suggested for the superluminous central object R136a alone, and with the H II region luminosity. With reference to related regions in the Galaxy, the likelihood that many of the brightest objects in 30 Dor are multiple systems is emphasized. An interpretation of R136a as a system containing a few very massive stars (as opposed to a single supermassive object) is in good accord with the observations, including the visual micrometer results. The study of 30 Dor and its central cluster is vital for an understanding of the numerous apparently similar regions now being discovered in more distant galaxies.

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Mid-Infrared (4.8–12.4 and 20.0 μm) Imaging of the Galactic Center: Modeling the Dust Emission and Energetics of the Central Parsec

Symposium - International Astronomical Union ◽

10.1017/s0074180900229732 ◽

1996 ◽

Vol 169 ◽

pp. 231-240 ◽

Cited By ~ 2

Author(s):

Dan Gezari ◽

Eli Dwek ◽

Frank Varosi

Keyword(s):

Galactic Center ◽

Dust Emission ◽

Infrared Emission ◽

Mid Infrared ◽

New Model ◽

Central Engine ◽

Direct Indication ◽

Sgr A ◽

Central Parsec ◽

Array Camera

We have modeled the mid-infrared emission from the Galactic Center using our array camera images at eight wavelengths. The results suggest that the high infrared luminosity of the region is provided by a cluster of luminous stars. There is no direct indication in the new model results of a very luminous object or “central engine” near Sgr A∗.

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Infrared Analysis of Supernova Remnants

International Astronomical Union Colloquium ◽

10.1017/s0252921100102672 ◽

1988 ◽

Vol 101 ◽

pp. 363-378 ◽

Cited By ~ 1

Author(s):

Eli Dwek

Keyword(s):

Supernova Remnants ◽

Infrared Emission ◽

Infrared Analysis ◽

Atomic Processes ◽

Infrared Observations ◽

X Ray ◽

Physical Conditions ◽

The Galaxy ◽

Dust Grain ◽

Astronomical Satellite

AbstractInfrared observations of supernova remnants obtained with the Infrared Astronomical Satellite provide new insights into the dynamics and energetics of the remnants, and into their interaction with the ambient interstellar medium. In most remnants the infrared emission arises from dust that is collisionally heated by the X-ray emitting gas. The infrared observations can therefore be used as a diagnostic for the physical conditions of the shocked gas. In particular, it is shown that all the prominent X-ray remnants in the Galaxy and in the LMC cool mainly by dust grain collisions instead of atomic processes.

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Diffraction Limited Near Infrared Imaging of the Central Parsec of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900107983 ◽

1994 ◽

Vol 158 ◽

pp. 379-381

Author(s):

A. Eckart ◽

R. Genzel ◽

R. Hofmann ◽

B.J. Sams ◽

L.E. Tacconi-Garman

Keyword(s):

Near Infrared ◽

Infrared Imaging ◽

Core Radius ◽

The Galaxy ◽

K 13 ◽

Sgr A ◽

Central Parsec ◽

Stellar Sources ◽

Stellar Density ◽

Source Number

We present deep 1.6 and 2.2 μm images of the central parsec of the Galaxy at a resolution of 0.15″. Most of the flux in earlier seeing limited images comes from about 340 unresolved stellar sources with K≤14. The IRS 16 and 13 complexes are resolved into about two dozen and half a dozen sources, a number of which are probably luminous hot stars. We confirm the presence of a blue near infrared object (K≈13) at the position of the compact radio source Sgr A∗. The spatial centroid of the source number distribution is consistent with the position of Sgr A∗ but not with a position in the IRS 16 complex. The stellar surface density in the central 10″ is very well fitted by an isothermal cluster model with a well defined core radius. The derived core radius of all 340 sources is 0.15±0.05 pc. The central stellar density is a few times 107 M⊙ pc−3. Buildup of massive stars by merging of lower mass stars and collisional disruption of giant atmospheres are very probable processes in the central 0.2 pc.

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Determination of the C/M5+ Ratio in the Galactic Disk

International Astronomical Union Colloquium ◽

10.1017/s025292110002203x ◽

1995 ◽

Vol 148 ◽

pp. 276-279

Author(s):

Francisco J. Fuenmayor

Keyword(s):

Near Infrared ◽

Galactic Center ◽

Galactic Disk ◽

Mean Value ◽

Galactocentric Distance ◽

The Galaxy ◽

Metal Abundance ◽

Objective Prism ◽

M Stars

AbstractA determination of the C/M5+ ratio, as a function of the galactocentric distance, in the galactic disk is presented. These results are based upon previous determinations of the space density for cool carbon stars and for late giant M stars in the Milky Way. Most of these results were obtained from objective-prism surveys in the near infrared using mainly Schmidt-type telescopes. The ratio C/M5+ appears to increase from 0.05 to 0.25 in the galactic disk, from the galactic center outwards. A mean value of 0.15 of this ratio for the Galaxy is suggested. Correlations between the C/M5+ ratio and currently known metal abundance gradients in the galactic disk are discussed.

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The Near Infrared Properties of Selected WN Stars in the Large Magellanic Cloud

Symposium - International Astronomical Union ◽

10.1017/s0074180900028928 ◽

1982 ◽

Vol 99 ◽

pp. 231-235

Author(s):

N. Panagia ◽

E.G. Tanzi ◽

M. Tarenghi

Keyword(s):

Near Infrared ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Infrared Photometry ◽

Central Object ◽

30 Doradus

We report here on preliminary infrared photometry of six WN stars in the Large Magellanic Cloud. Besides R136, the central object of the 30 Doradus Nebula, the sample includes three stars (R139, R140, R145) located near the center of the region (within ∼ 1 arcmin) and two more stars (R144, R147) at a distance of ∼ 5 arcmin from R136.

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7.3. Sgr A∗ in the mid-infrared reference frame: no evidence of an infrared counterpart, or interaction with nearby sources

Symposium - International Astronomical Union ◽

10.1017/s0074180900084990 ◽

1998 ◽

Vol 184 ◽

pp. 295-297

Author(s):

Dan Gezari

Keyword(s):

Near Infrared ◽

Reference Frames ◽

A Priori ◽

Infrared Emission ◽

Mid Infrared ◽

Source Component ◽

Comparable Accuracy ◽

Sgr A ◽

Central Parsec ◽

Infrared Sources

We have determined the position of Sgr A∗ with respect to the mid-infrared (5-25 m) sources in the central parsec by direct correlation of our 12.4 m array image (Gezari et al. 1994) and the new 2-cm continuum VLA map (Yusef-Zadeh 1997; private communication), without a priori knowledge of any other position determinations. Menten et al. (1997) recently succeeded in registering the radio and near-infrared (2.2 m) reference frames with high precision (+0.03 arcsec) using VLA observations of Sgr A∗, SiO masers and H2O masers. Unfortunately, registering the mid-infrared and radio reference frames with comparable accuracy cannot be done by applying the 2.2 m calibration. Most near-infrared sources have no detectable mid-infrared counterparts, and it is not obvious which of those that do are coincident (if any), since near-infrared and mid-infrared emission generally does not arise from the same physical source component. Dramatic examples of shifts between the brightest near- and mid-infrared peaks can be seen in Orion BN/KL and the Ney-Allen Nebula (Gezari and Backman 1994; Gezari, Backman and Werner 1997) corresponding to 0.1 - 0.5 arcsec if they were located at 8.5 kpc. Further, several Sgr A West IRS sources are displaced significantly in the infrared and radio, suggesting they may actually be compact clusters of objects.

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Systematic opacity calculations for kilonovae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1576 ◽

2020 ◽

Vol 496 (2) ◽

pp. 1369-1392 ◽

Cited By ~ 9

Author(s):

Masaomi Tanaka ◽

Daiji Kato ◽

Gediminas Gaigalas ◽

Kyohei Kawaguchi

Keyword(s):

Near Infrared ◽

Thermal Emission ◽

Energy Levels ◽

Blue Emission ◽

Electron Shell ◽

Infrared Emission ◽

Atomic Data ◽

High Electron ◽

R Process ◽

Process Elements

ABSTRACT Coalescence of neutron stars (NSs) gives rise to kilonova, thermal emission powered by radioactive decays of freshly synthesized r-process nuclei. Although observational properties are largely affected by bound–bound opacities of r-process elements, available atomic data have been limited. In this paper, we study element-to-element variation of the opacities in the ejecta of NS mergers by performing systematic atomic structure calculations of r-process elements for the first time. We show that the distributions of energy levels tend to be higher as electron occupation increases for each electron shell due to the larger energy spacing caused by larger effects of spin–orbit and electron–electron interactions. As a result, elements with a fewer number of electrons in the outermost shells tend to give larger contributions to the bound–bound opacities. This implies that Fe is not representative for the opacities of light r-process elements. The average opacities for the mixture of r-process elements are found to be κ ∼ 20–30 cm2 g−1 for the electron fraction of Ye ≤ 0.20, κ ∼ 3–5 cm2 g−1 for Ye = 0.25–0.35, and κ ∼ 1 cm2 g−1 for Ye = 0.40 at $T = 5000\!-\!10\, 000$ K, and they steeply decrease at lower temperature. We show that, even with the same abundance or Ye, the opacity in the ejecta changes with time by one order of magnitude from 1 to 10 d after the merger. Our radiative transfer simulations with the new opacity data confirm that ejecta with a high electron fraction (Ye ≳ 0.25, with no lanthanide) are needed to explain the early, blue emission in GW170817/AT2017gfo while lanthanide-rich ejecta (with a mass fraction of lanthanides ∼5 × 10−3) reproduce the long-lasting near-infrared emission.

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