scholarly journals The infrared K-band identification of the DSO/G2 source from VLT and Keck data

2013 ◽  
Vol 9 (S303) ◽  
pp. 269-273
Author(s):  
A. Eckart ◽  
M. Horrobin ◽  
S. Britzen ◽  
M. Zamaninasab ◽  
K. Mužić ◽  
...  
Keyword(s):  
Fast Moving ◽  
Near Infrared ◽  
Dust Cloud ◽  
Continuum Emission ◽  
Proper Motions ◽  
Infrared Excess ◽  
Sagittarius A ◽  
Band Emission ◽  
Sgr A ◽  
Data Result

AbstractA fast moving infrared excess source (G2) which is widely interpreted as a core-less gas and dust cloud approaches Sagittarius A* (Sgr A*) on a presumably elliptical orbit. VLT Ks-band and Keck K′-band data result in clear continuum identifications and proper motions of this ∼19m Dusty S-cluster Object (DSO). In 2002-2007 it is confused with the star S63, but free of confusion again since 2007. Its near-infrared (NIR) colors and a comparison to other sources in the field speak in favor of the DSO being an IR excess star with photospheric continuum emission at 2 microns than a core-less gas and dust cloud. We also find very compact L′-band emission (<0.1″) contrasted by the reported extended (0.03″ up to ∼0.2″ for the tail) Brγ emission. The presence of a star will change the expected accretion phenomena, since a stellar Roche lobe may retain a fraction of the material during and after the peri-bothron passage.

scholarly journals Nature of the Dusty S-cluster Object (DSO/G2): Pre-main-sequence star with non-spherical dusty envelope

2016 ◽  
Vol 11 (S322) ◽  
pp. 231-232
Author(s):  
M. Zajaček ◽  
M. Valencia-S. ◽  
B. Shahzamanian ◽  
F. Peissker ◽  
A. Eckart ◽  
...  
Keyword(s):  
Energy Distribution ◽  
Main Sequence ◽  
Near Infrared ◽  
Spectral Energy Distribution ◽  
Main Sequence Star ◽  
Continuum Emission ◽  
Spectral Energy ◽  
Galactic Centre ◽  
Infrared Excess ◽  
Sgr A

AbstractNear-infrared observations reveal several infrared-excess sources near the Galactic Centre with emission lines present in their spectra. One of these objects, DSO/G2, which moves around the supermassive black hole (Sgr A*) on a highly eccentric orbit, passed the pericentre at approximately 160 AU in 2014. It remained compact, which implies that at least in this case it is a star embedded in a dusty envelope. The spectral energy distribution and the detection of polarized continuum emission indicate that it is probably a pre-main-sequence star surrounded by a dense envelope with bipolar cavities. In addition, the star associated with DSO/G2 plausibly develops a bow shock due to its supersonic motion. The model of the star surrounded by the non-spherical dusty envelope can reproduce the main characteristics of the DSO/G2 source: 1. spectral energy distribution in near-infrared bands; 2. linear polarization in Ks band; and 3. the overall compact behaviour.

scholarly journals Detection of polarized continuum emission of the Dusty S-cluster Object (DSO/G2)

2016 ◽  
Vol 11 (S322) ◽  
pp. 233-234
Author(s):  
B. Shahzamanian ◽  
M. Zajaček ◽  
M. Valencia-S. ◽  
F. Peissker ◽  
A. Eckart ◽  
...  
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Continuum Emission ◽  
Polarization Angle ◽  
Imaging Data ◽  
Intrinsic Geometry ◽  
Infrared Excess ◽  
Geometrical Properties ◽  
Sgr A ◽  
First Time

AbstractA peculiar source in the Galactic center known as the Dusty S-cluster Object (DSO/G2) moves on a highly eccentric orbit around the supermassive black hole with the pericenter passage in the spring of 2014. Its nature has been uncertain mainly because of the lack of any information about its intrinsic geometry. For the first time, we use near-infrared polarimetric imaging data to obtain constraints about the geometrical properties of the DSO. We find out that DSO is an intrinsically polarized source, based on the significance analysis of polarization parameters, with the degree of the polarization of ~30% and an alternating polarization angle as it approaches the position of Sgr A*. Since the DSO exhibits a near-infrared excess of Ks-L′ > 3 and remains rather compact in emission-line maps, its main characteristics may be explained with the model of a pre-main-sequence star embedded in a non-spherical dusty envelope.

scholarly journals Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic center

2013 ◽  
Vol 551 ◽  
pp. A18 ◽  
Author(s):  
A. Eckart ◽  
K. Mužić ◽  
S. Yazici ◽  
N. Sabha ◽  
B. Shahzamanian ◽  
...  
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Proper Motions ◽  
Infrared Excess

scholarly journals Near-infrared monitoring of the accretion outburst in the massive young stellar object S255-NIRS3

2019 ◽  
Vol 72 (1) ◽  
Author(s):  
Mizuho Uchiyama ◽  
Takuya Yamashita ◽  
Koichiro Sugiyama ◽  
Tatsuya Nakaoka ◽  
Miho Kawabata ◽  
...  
Keyword(s):  
Light Curve ◽  
Near Infrared ◽  
Stellar Object ◽  
Young Stellar Objects ◽  
Infrared Light ◽  
Continuum Emission ◽  
Sudden Increase ◽  
Maser Emission ◽  
Young Stellar Object ◽  
Band Emission

Abstract We followed up the massive young stellar object S255-NIRS3 (= S255-IRS1b) during its recent accretion outburst event in the $K_{\rm s}$ band with Kanata/HONIR for four years after its burst and obtained a long-term light curve. This is the most complete near-infrared light curve of the S255-NIRS3 burst event that has ever been presented. The light curve showed a steep increase reaching a peak flux that was 3.4 mag brighter than the quiescent phase and then a relatively moderate year-scale fading until the last observation, similar to that of the accretion burst events such as EXors found in lower-mass young stellar objects. The behavior of the $K_{\rm s}$-band light curve is similar to that observed in 6.7 GHz class II methanol maser emission, with a sudden increase followed by moderate year-scale fading. However, the maser emission peaks appear 30–50 d earlier than that of the $K_{\rm s}$ band emission. The similarities confirmed that the origins of the maser emission and the $K_{\rm s}$-band continuum emission are common, as previously shown from other infrared and radio observations by Stecklum et al. (2016, Astronomer’s Telegram, 8732), Caratti o Garatti et al. (2017b, Nature Phys., 13, 276), and Moscadelli et al. (2017, A&A, 600, L8). However, the differences in energy transfer paths, such as the exciting/emitting/scattering structures, may cause the delay in the flux-peak dates.

scholarly journals SiO and H2O Masers in the Central Parsec of the Galaxy

1998 ◽  
Vol 164 ◽  
pp. 229-230 ◽  
Author(s):  
Karl M. Menten ◽  
Mark J. Reid
Keyword(s):  
Galactic Center ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Proper Motions ◽  
Infrared Images ◽  
Evolved Stars ◽  
The Galaxy ◽  
Sgr A ◽  
Central Parsec ◽  
Infrared Sources

AbstractWe have discovered maser emission from SiO and H2O molecules toward a number of evolved stars within the central parsec of our Galaxy. The maser positions can be registered with milliarcsecond precision relative to the radio continuum emission of the nonthermal Galactic center source Sgr A*. Since the masing stars are prominent infrared sources, our data can be used to locate the position of Sgr A* on infrared images of the Galactic center region. Using VLBA observations it will be possible to measure proper motions of the maser stars, which can be used to put constraints on the mass distribution in the central parsec.

The IGRINS YSO Survey II: Veiling Spectra of Pre-main-sequence Stars in Taurus-Auriga

2021 ◽  
Vol 922 (1) ◽  
pp. 27
Author(s):  
Benjamin Kidder ◽  
Gregory Mace ◽  
Ricardo López-Valdivia ◽  
Kimberly Sokal ◽  
Victoria E. Catlett ◽  
...  
Keyword(s):  
Near Infrared ◽  
Thermal Emission ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Class Iii ◽  
Infrared Excess ◽  
Stellar Objects ◽  
Star Forming ◽  
Infrared Spectrometer ◽  
Low Mass

Abstract We present measurements of the H- and K-band veiling for 141 young stellar objects (YSOs) in the Taurus-Auriga star-forming region using high-resolution spectra from the Immersion Grating Near-Infrared Spectrometer. In addition to providing measurements of r H and r K , we produce low-resolution spectra of the excess emission across the H and K bands. We fit temperatures to the excess spectra of 46 members of our sample and measure near-infrared excess temperatures ranging from 1200–2200 K, with an average of 1575 ± 225 K. We compare the luminosity of the excess continuum emission in Class II and Class III YSOs and find that a number of Class III sources display a significant amount of excess flux in the near-infrared. We conclude that the mid-infrared SED slope, and therefore young stellar object classification, is a poor predictor of the amount of near-infrared veiling. If the veiling arises in thermal emission from dust, its presence implies a significant amount of remaining inner-disk (<1 au) material in these Class III sources. We also discuss the possibility that the veiling effects could result from massive photospheric spots, unresolved binary companions, or accretion emission. Six low-mass members of our sample contain a prominent feature in their H-band excess spectra that is consistent with veiling from cool photospheric spots.

scholarly journals Event horizon scale emission models for Sagittarius A*

2013 ◽  
Vol 9 (S303) ◽  
pp. 298-302
Author(s):  
J. Dexter
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Near Infrared ◽  
Sagittarius A ◽  
Long Baseline ◽  
Black Hole Accretion ◽  
Emission Models ◽  
Infrared Interferometry ◽  
Sgr A

AbstractVery long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.

scholarly journals Near infrared variability of Sgr A* - spectral index measurements

2013 ◽  
Vol 9 (S303) ◽  
pp. 274-282 ◽  
Author(s):  
G. Witzel ◽  
M. Morris ◽  
A. Ghez ◽  
L. Meyer ◽  
E. Becklin ◽  
...  
Keyword(s):  
Spectral Index ◽  
Near Infrared ◽  
Time Lag ◽  
Time Variable ◽  
Time Variability ◽  
Data Set ◽  
Sagittarius A ◽  
State Process ◽  
Sgr A ◽  
High Cadence

AbstractWe discuss observations of Sagittarius A* with NACO@VLT in K-band and recent synchronous observations with NIRC2@Keck II and OSIRIS@Keck I in L′-band and H-band, respectively. The variability of Sagittarius A* in the near infrared is a continuous one-state process that can be described by a pure red-noise process having a timescale of a few hours. We describe this process and its properties in detail. Our newest observations with the Keck telescopes represent the first truly synchronous high cadence data set to test for time variability of the spectral index within the near infrared. We discovered a time-variable spectral index that might be interpreted as a time lag of the L′-band with respect to the H-band.

scholarly journals Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed

2020 ◽  
Vol 636 ◽  
pp. A25
Author(s):  
E. Mossoux ◽  
B. Finociety ◽  
J.-M. Beckers ◽  
F. H. Vincent
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Milky Way ◽  
Detection Efficiency ◽  
Previous Method ◽  
Arrival Times ◽  
X Ray ◽  
Sagittarius A ◽  
Block Algorithm ◽  
Sgr A

Context. The supermassive black hole Sagittarius A* (Sgr A*) is located at the dynamical center of the Milky Way. In a recent study of the X-ray flaring activity from Sgr A* using Chandra, XMM-Newton, and Swift observations from 1999 to 2015, it has been argued that the bright flaring rate has increased from 2014 August 31 while the faint flaring rate decreased from around 2013 August. Aims. We tested the persistence of these changes in the flaring rates with new X-ray observations of Sgr A* performed from 2016 to 2018 (total exposure of 1.4 Ms). Methods. We reprocessed the Chandra, XMM-Newton, and Swift observations from 2016 to 2018. We detected 9 flares in the Chandra data and 5 flares in the Swift data that we added to the set of 107 previously detected flares. We computed the intrinsic distribution of flare fluxes and durations corrected for the sensitivity bias using a new method that allowed us to take the error on the flare fluxes and durations into account. From this intrinsic distribution, we determined the average flare detection efficiency for each Chandra, XMM-Newton, and Swift observation. After correcting each observational exposure for this efficiency, we applied the Bayesian blocks algorithm on the concatenated flare arrival times. As in the above-mentioned study, we also searched for a flux and fluence threshold that might lead to a change in flaring rate. We improved the previous method by computing the average flare detection efficiencies for each flux and fluence range. Results. The Bayesian block algorithm did not detect any significant change in flaring rate of the 121 flares. However, we detected an increase by a factor of about three in the flaring rate of the most luminous and most energetic flares that have occurred since 2014 August 30. Conclusions. The X-ray activity of Sgr A* has increased for more than four years. Additional studies about the overall near-infrared and radio behavior of Sgr A* are required to draw strong results on the multiwavelength activity of the black hole.

scholarly journals Short-term variability of Sgr A*

2006 ◽  
Vol 2 (S238) ◽  
pp. 195-200
Author(s):  
M. R. Morris ◽  
S. D. Hornstein ◽  
A. M. Ghez ◽  
J. R. Lu ◽  
K. Matthews ◽  
...  
Keyword(s):  
Time Scale ◽  
Near Infrared ◽  
Accretion Rate ◽  
Outer Boundary ◽  
Radial Distance ◽  
Emission Region ◽  
Sagittarius A ◽  
Dynamical Time ◽  
Galactic Black Hole ◽  
Sgr A

AbstractObservations of Sgr A* over the past 4 years with the Keck Telescope in the near-infrared, coupled with millimeter and submillimeter observations, show that the 3.7×106M⊙Galactic Black Hole, Sagittarius A*, displays continuous variability at all these wavelengths, with the variability power concentrated on characteristic time scales of a few hours, and with a variability fraction that increases with wavelength. We review the observations indicating that the few-hour time scale for variability is reproduced at all accessible wavelengths. Interpreted as a dynamical time, this time scale corresponds to a radial distance of 2 AU, or ∼25 Schwarzschild radii. Searches for quasi-periodicities in the near-infrared data from the Keck Telescope have so far been negative. One interpretation of the character of these variations is that they result from a recurring disk instability, rather than from variations in the mass accretion rate flowing through the outer boundary of the emission region. However, neither a variable accretion rate nor a mechanism associated with a jet can presently be ruled out.

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