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We present near-infrared H-, K-, L- and M-band photometry of the Galactic Center from images obtained at the ESO VLT in May and August 2002, using the NAOS/CONICA (H and K) and the ISAAC (L and M) instruments. The large field of view (70" x 70") of the ISAAC instrument and the large number of sources identified (L-M data for 541 sources) allows us...
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... the median, which also effectively removed cosmic rays and bad pixels. The final images were then created by coaddition of the me- dian images with the best effective seeing, i.e. better than 0.6 ′′ , resulting in total integration times of 229.7 s for the L-band image and 162.4 s for the M-band image. The final M-band image is shown in Fig. 1. Finally, PSF-fitting photometry was performed on all four final images using the IRAF/DAOPHOT software ...
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Citations
... .9, and assuming a typical extinction power law varying as A(V ) ∝ λ −1.75 (Draine 1989; and see Doherty et al. 1994;Viehmann et al. 2005;Dong et al. 2017;Uyama et al. 2020 for examples of papers that use that technique), we obtain A(K s ) ∼ 0.85 and ¢Ã L 0.32 ( ) (via a simple cross product). Therefore, K s and ¢ L are not strongly impacted by dust reddening; such an extinction results in a color shift of The 21 sources detected with S/N > 5 when computing the signal-to-noise map are labeled. ...
X-ray binaries provide exceptional laboratories for understanding the physics of matter under the most extreme conditions. Until recently, there were few, if any, observational constraints on the circumbinary environments of X-ray binaries at ∼100–5000 au scales. It remains unclear how the accretion onto the compact objects or the explosions giving rise to the compact objects interact with their immediate surroundings. Here, we present the first high-contrast adaptive optics images of X-ray binaries. These observations target all X-ray binaries within ∼3 kpc accessible with the Keck/NIRC2 vortex coronagraph. This paper focuses on one of the first key results from this campaign; our images reveal the presence of 21 sources potentially associated with the γ Cassiopeiae analog high-mass X-ray binary RX J1744.7−2713. By conducting different analyses—a preliminary proper motion analysis, a color–magnitude diagram, and a probability of chance alignment calculation—we found that three of these 21 sources have a high probability of being bound to the system. If confirmed, they would be in wide orbits (∼450 to 2500 au). While follow-up astrometric observations will be needed in ∼5–10 yr to confirm further the bound nature of these detections, these discoveries emphasize that such observations may provide a major breakthrough in the field. In fact, they would be useful not only for our understanding of stellar multiplicity, but also for our understanding of how planets, brown dwarfs, and stars can form even in the most extreme environments.
... Ho we ver, in case of large uncertainty in the spectrophotometric measurements of individual sources due to low S/N and uncertainties in continuum determination (Chiar et al. 2002 ;Moultaka et al. 2004 ;Godard et al. 2012 ), or presence of intrinsic spectral properties through some lines of sight, there might be source-to-source variations. There might also be bias in the measurements since some of the GC sources are known that they have thick circumstellar dust shells (Roche & Aitken 1985 ;Tanner et al. 2005 ;Viehmann et al. 2005 ;Pott et al. 2008 ;Moultaka, Eckart & Sch ödel 2009 ) and there are also many sources that are problematic to classify (Buchholz, Sch ödel & Eckart 2009 ;Hanson & Bailer-Jones 2014 ;Dong et al. 2017 ;Nogueras-Lara et al. 2018 ). Ho we ver, the uniformity in our measurements suggests that the aliphatic hydrocarbon absorption is dominated by material distributed along the sightline in DISM rather than local to each source, and so our method measures large-scale properties of the foreground molecular medium. ...
We implement a new observational method for mapping the aliphatic hydrocarbon content in the solid phase in our Galaxy, based on spectrophotometric imaging of the 3.4 μm absorption feature from interstellar dust. We previously demonstrated this method in a field including the Galactic Centre cluster. We applied the method to a new field in the Galactic centre where the 3.4 μm absorption feature has not been previously measured and we extended the measurements to a field in the Galactic plane to sample the diffuse local interstellar medium, where the 3.4 μm absorption feature has been previously measured. We have analysed 3.4 μm optical depth and aliphatic hydrocarbon column density maps for these fields. Optical depths are found to be reasonably uniform in each field, without large source-to-source variations. There is, however, a weak trend towards increasing optical depth in a direction towards b = 0○ in the Galactic centre. The mean value of column densities and abundances for aliphatic hydrocarbon were found to be about several $\rm \times 10^{18} \, cm^{-2}$ and several tens × 10−6, respectively for the new sightlines in the Galactic plane. We conclude that at least 10–20 per cent of the carbon in the Galactic plane lies in aliphatic form.
... , and assuming a typical extinction power law varying as A(V ) ∝ λ −1.75 (Draine 1989; and see Doherty et al. 1994;Viehmann et al. 2005;Dong et al. 2017;Uyama et al. 2020 for examples of papers that use that technique), we obtain A(K s ) ∼ 0.85 and A(L ) ∼ 0.32 (via a simple cross product). Therefore, K s and L are not strongly impacted by dust reddening; such an extinction results in a color shift of ∼ 0.5 mag for K s − L and a magnitude shift of ∼ 0.3 for L . ...
X-ray binaries provide exceptional laboratories for understanding the physics of matter under the most extreme conditions. Until recently, there were few, if any, observational constraints on the circumbinary environments of X-ray binaries at $\sim$ 100-5000 AU scales; it remains unclear how the accretion onto the compact objects or the explosions giving rise to the compact objects interact with their immediate surroundings. Here, we present the first high-contrast adaptive optics images of X-ray binaries. These observations target all X-ray binaries within $\sim$ 3 kpc accessible with the Keck/NIRC2 vortex coronagraph. This paper focuses on one of the first key results from this campaign: our images reveal the presence of 21 sources potentially associated with the $\gamma$ Cassiopeiae analog high-mass X-ray binary RX J1744.7$-$2713. By conducting different analyses - a preliminary proper motion analysis, a color-magnitude diagram and a probability of chance alignment calculation - we found that three of these 21 sources have a high probability of being bound to the system. If confirmed, they would be in wide orbits ($\sim$ 450 AU to 2500 AU). While follow-up astrometric observations will be needed in $\sim$ 5-10 years to confirm further the bound nature of these detections, these discoveries emphasize that such observations may provide a major breakthrough in the field. In fact, they would be useful not only for our understanding of stellar multiplicity but also for our understanding of how planets, brown dwarfs and stars can form even in the most extreme environments.
... Even though there have been many photometric studies on stars in the GC in various other wavelengths, they are limited in the MIR (e.g., Blum et al. 1996;Ott et al. 1999;Tanner et al. 2002;Viehmann et al. 2005Viehmann et al. , 2006. We carry on these studies on the extended dusty sources that we have identified. ...
... Although it is a stellar core, the extended source is not circularly symmetric, which has been a topic of interest. Viehmann et al. (2005) suggests that this morphology is due to a bow shock generated by winds from the massive central stellar cluster or an outflow from Sgr A * . However, Yusef-Zadeh et al. (2017) suggests a tidal distortion scenario as IRS 3 orbits around Sgr A * . ...
Mid-infrared (MIR) images of the Galactic center show extended gas and dust features along with bright infrared sources (IRS). Some of these dust features are a part of ionized clumpy streamers orbiting Sgr A*, known as the mini-spiral. We present their proper motions over a 12 yr time period and report their flux densities in N -band filters and derive their spectral indices. The observations were carried out by VISIR at the ESO’s Very Large Telescope. High-pass filtering led to the detection of several resolved filaments and clumps along the mini-spiral. Each source was fit by a 2D Gaussian profile to determine the offsets and aperture sizes. We perform aperture photometry to extract fluxes in two different bands. We present the proper motions of the largest consistent set of resolved and reliably determined sources. In addition to stellar orbital motions, we identify a stream-like motion of extended clumps along the mini-spiral. We also detect MIR counterparts of the radio tail components of the IRS 7 source. They show a clear kinematical deviation with respect to the star. They likely represent Kelvin–Helmholtz instabilities formed downstream in the shocked stellar wind. We also analyze the shape and orientation of the extended late-type IRS 3 star that is consistent with the Atacama Large Millimeter/submillimeter Array submillimeter detection of the source. Its puffed-up envelope with a radius of ∼2 × 10 ⁶ R ⊙ could be the result of the red-giant collision with a nuclear jet, which was followed by tidal prolongation along the orbit.
... Even though there have been many photometric studies on stars in the galactic center in various other wavelengths, they are limited in MIR (e.g. Blum et al. 1996;Ott et al. 1999;Tanner et al. 2002;Viehmann et al. 2005Viehmann et al. , 2006. We carry on these studies on the extended dusty sources that we have identified. ...
... Albeit the stellar core, the extended source is not circularly symmetric which has been a topic of interest. Viehmann et al. (2005) suggest that this morphology is due to a bow shock generated by winds from the massive central stellar cluster or an outflow from Sgr A*. However, Yusef-Zadeh et al. (2017) suggests a tidal distortion scenario as IRS3 orbits around Sgr A*. ...
Mid-Infrared (MIR) images of the Galactic center show extended gas and dust features along with bright IRS sources. Some of these dust features are a part of ionized clumpy streamers orbiting Sgr~A*, known as the mini-spiral. We present their proper motions over 12 year time period and report their flux densities in $N$-band filters {and derive their spectral indices}. The observations were carried out by VISIR at ESO VLT. High-pass filtering led to the detection of several resolved filaments and clumps along the mini-spiral. Each source was fit by a 2-D Gaussian profile to determine the offsets and aperture sizes. We perform aperture photometry to extract fluxes in two different bands. We present the proper motions of the largest consistent set of resolved and reliably determined sources. In addition to stellar orbital motions, we identify a stream-like motion of extended clumps along the mini-spiral. We also detect MIR counterparts of the radio tail components of the IRS7 source. They show a clear kinematical deviation with respect to the star. They likely represent Kelvin-Helmholtz instabilities formed downstream in the shocked stellar wind. We also analyze the shape and the orientation of the extended late-type IRS3 star that is consistent with the ALMA sub-mm detection of the source. Its puffed-up envelope with the radius of $\sim 2\times 10^6\,R_{\odot}$ could be the result of the red-giant collision with a nuclear jet, which was followed by the tidal prolongation along the orbit.
... Observations of the central stellar cluster have discovered a large population of mainly late-type red giant stars, including asymptotic giant branch (AGB) stars (see e.g. [6,7,8,9,10]). Spectroscopic observations have found hot, early-type stars with H, He, and N emission lines showing characteristics of post main-sequence Ofpe/WN9, luminous blue variables (LBVs) and Wolf-Rayet stars [11,12,13,7,14,8]. ...
... [6,7,8,9,10]). Spectroscopic observations have found hot, early-type stars with H, He, and N emission lines showing characteristics of post main-sequence Ofpe/WN9, luminous blue variables (LBVs) and Wolf-Rayet stars [11,12,13,7,14,8]. ...
... We also referred to the lists of previously known stellar sources in the central parsec observed at 43 GHz and in IR observations [7,51,48] to verify the positions of detected candidates. After this process, 5 sources were confirmed in the ATCA data and 20 sources in the ALMA data. ...
... Observations of the central stellar cluster have discovered a large population of mainly late-type red giant stars, including asymptotic giant branch (AGB) stars (see e.g. [6,7,8,9,10]). Spectroscopic observations have found hot, early-type stars with H, He, and N emission lines showing characteristics of post main-sequence Ofpe/WN9, luminous blue variables (LBVs) and Wolf-Rayet stars [11,12,13,7,14,8]. ...
... [6,7,8,9,10]). Spectroscopic observations have found hot, early-type stars with H, He, and N emission lines showing characteristics of post main-sequence Ofpe/WN9, luminous blue variables (LBVs) and Wolf-Rayet stars [11,12,13,7,14,8]. ...
... These are excluded from the search of SiO maser candidate sources. We also referred to the lists of previously known stellar sources in the central parsec observed at 43 GHz and in IR observations [7,51,48] to verify the positions of detected candidates. After this process, 5 sources were confirmed in the ATCA data and 20 sources in the ALMA data. ...
We present results of 3 mm observations of SiO maser sources in the Galactic Centre (GC) from observations with the Australia Telescope Compact Array between $2010-2014$, along the transitions of the SiO molecule at $v = 1, J = 2-1$ at 86.243 GHz and $v = 2, J = 2-1$ at 85.640 GHz. We also present the results of the 3 mm observations with Atacama Large Millimeter/Submillimeter Array (ALMA). We detected 5 maser sources from the ATCA data, IRS 7, IRS 9, IRS 10EE, IRS 12N, and IRS 28; and 20 sources from the ALMA data including 4 new sources. These sources are predominantly late-type giants or emission line stars with strong circumstellar maser emission. We analyse these sources and calculate their proper motions. We also study the variability of the maser emission. IRS 7, IRS 12N and IRS 28 exhibit long period variability of the order of $1 - 2$ years, while other sources show steady increase or decrease in flux density and irregular variability over observation timescales. This behaviour is consistent with the previous observations.
... The red point indicates the observation highlighted on top. shock source originating from IRS 3 ( Viehmann et al. 2005;Yusef-Zadeh et al. 2017). The filaments could be responsible for the long-term flux dips observed in these two stars' light curves. ...
We present an ≈11.5 yr adaptive optics (AO) study of stellar variability and search for eclipsing binaries in the central ∼0.4 pc (∼10″) of the Milky Way nuclear star cluster. We measure the photometry of 563 stars using the Keck II NIRC2 imager (K′-band, λ 0 = 2.124 μm). We achieve a photometric uncertainty floor of Δm K′ ∼ 0.03 (≈3%), comparable to the highest precision achieved in other AO studies. Approximately half of our sample (50% ± 2%) shows variability: 52% ±5% of known early-type young stars and 43% ±4% of known late-type giants are variable. These variability fractions are higher than those of other young, massive star populations or late-type giants in globular clusters, and can be largely explained by two factors. First, our experiment time baseline is sensitive to long-term intrinsic stellar variability. Second, the proper motion of stars behind spatial inhomogeneities in the foreground extinction screen can lead to variability. We recover the two known Galactic center eclipsing binary systems: IRS 16SW and S4-258 (E60). We constrain the Galactic center eclipsing binary fraction of known early-type stars to be at least 2.4% ±1.7%. We find no evidence of an eclipsing binary among the young S-stars nor among the young stellar disk members. These results are consistent with the local OB eclipsing binary fraction. We identify a new periodic variable, S2-36, with a 39.43 days period. Further observations are necessary to determine the nature of this source. © 2019. The American Astronomical Society. All rights reserved.
Velocity profiles of a line of at 3.7 μ m produced in warm diffuse gas have been observed toward 18 stars in the Central Molecular Zone (CMZ) of the Galaxy. Their longitude–velocity diagram indicates that the gas is radially expanding within the CMZ at speeds up to a maximum of ∼150 km s ⁻¹ . The current momentum and energy in the gas are ∼5 × 10 ⁸ M ⊙ km s ⁻¹ and ∼5 × 10 ⁵³ erg. The motion is similar to that of the Expanding Molecular Ring discovered in 1972 by Kaifu et al. and by Scoville. We propose that the expanding gas seen in is part of the same phenomenon, despite differences in estimates of density, morphology, and degree of rotation. The outward motion suggests that one or more ejection events occurred near the center of the CMZ (0.5–1) × 10 ⁶ yr ago, which may be related to creation of the recently observed microwave bubble. These observations revive the circular face-on view of the CMZ proposed in 1972, which fell out of favor after 1991 when Binney et al. proposed that a face-on view of the CMZ would show it to have an elliptical shape, with high eccentricity. While that model may apply on kiloparsec scales, we argue that it is incorrect to apply it to the much smaller CMZ. We discuss the fate of the expanding gas, which appears to be eventual infall into the center, leading to episodes of star formation and violent events associated with accretion onto Sgr A*.
The molecular gas in the central molecular zone (CMZ) of the Galaxy has been studied using infrared absorption spectra of H 3 ⁺ lines at 3.5–4.0 μ m and CO lines near 2.34 μ m. In addition to the previously reported spectra of these lines toward eight stars located within 30 pc of Sgr A*, there are now spectra toward ∼30 bright stars located from 140 pc west to 120 pc east of Sgr A*. The spectra show the presence of warm ( T ∼ 200 K) and diffuse ( n < 100 cm ⁻³ ) gas with N (H 3 ⁺ ) ∼ 3 × 10 ¹⁵ cm ⁻² on the majority of sight lines. Instead of our previous analysis, in which only electrons from photoionization of carbon atoms were considered, we have developed a simple model calculation in which the cosmic-ray ionization of H 2 and H is also taken into account. We conclude the following: (1) Warm and diffuse gas dominates the volume of the CMZ. The volume filling factor of dense gas must be much less than 0.1, and the CMZ is not as opaque as previously considered. The X-ray-emitting ultrahot 10 ⁸ K plasma, which some thought to dominate the CMZ, does not exist over extended regions. (2) The cosmic-ray ionization rate is ζ ∼ 2 × 10 ⁻¹⁴ s ⁻¹ , higher than in Galactic dense clouds and diffuse clouds by factors of ∼1000 and ∼100, respectively. If the equipartition law stands, this suggests a pervading magnetic field on the order of ∼100 μ G.
