Dust embedded sources at the Galactic Center

Moultaka, J.; Eckart, A.; Viehmann, T.; Mouawad, N.; Straubmeier, C.; Ott, Thomas; Schödel, R.

doi:10.1051/0004-6361:20035807

Cited by 45 publications

(94 citation statements)

References 102 publications

(151 reference statements)

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“…Moultaka et al (2004) fitted the Lp-band spectrum of IRS 21 with a 1200 K blackbody, which is hotter than the value found for IRS 1W in the same study (∼900 K). This alone would lead to a higher emission at shorter wavelengths, and if dust emission is dominant for both sources, why is the polarization of IRS 1W and IRS 21 almost the same in the Ks-band, while the latter source has a much higher polarization in the Lp-band?…”

Section: Comparing the Bright Bow-shock Sourcesmentioning

confidence: 57%

Ks- andLp-band polarimetry on stellar and bow-shock sources in the Galactic center

Witzel

Schödel

Eckart

2013

A&A

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Context. Infrared observations of the Galactic center (GC) provide a unique opportunity to study stellar and bow-shock polarization effects in a dusty environment. Aims. The goals of this work are to present new Ks-and Lp-band polarimetry on an unprecedented number of sources in the central parsec of the GC, thereby expanding our previous results in the H-and Ks-bands. Methods. We use AO-assisted Ks-and Lp-band observations, obtained at the ESO VLT. High precision photometry and the new polarimetric calibration method for NACO allow us to map the polarization in a region of 8 × 25 (Ks) resp. 26 × 28 (Lp). These are the first polarimetric observations of the GC in the Lp-band in 30 years, with vastly improved spatial resolution compared to previous results. This allows resolved polarimetry on bright bow-shock sources in this area for the first time at this wavelength. Results. We find foreground polarization to be largely parallel to the Galactic plane (Ks-band: 6.1% at 20 • , Lp-band: 4.5% at 20 • ), in good agreement with our previous findings and with older results. The previously described Lp-band excess in the foregound polarization towards the GC could be confirmed here for a much larger number of sources. The bow-shock sources contained in the FOV seem to show a different relation between the polarization in the observed wavelength bands than what was determined for the foreground. This points to the different relevant polarization mechanisms. The resolved polarization patterns of IRS 5 and 10W match the findings we presented earlier for IRS 1W. Additionally, intrinsic Lp-band polarization was measured for IRS 1W and 21, as well as for other, less prominent mid-infrared-excess sources (IRS 2S, 2L, 5NE). The new data offer support for the presumed bow-shock nature of several of these sources (1W, 5, 5NE, 10W, 21) and for the model of bow-shock polarization presented in our last work.

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Section: Comparing the Bright Bow-shock Sourcesmentioning

confidence: 57%

Ks- andLp-band polarimetry on stellar and bow-shock sources in the Galactic center

Witzel

Schödel

Eckart

2013

A&A

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“…Water ice absorption at 3.0 µm and aliphatic hydrocarbon absorptions around 3.4 µm and at 3.48 µm have also been observed in the spectra of the bright sources located in the central parsec of the Galaxy: Jones et al (1983), Butchart et al (1986), McFadzean et al (1989), Sandford et al (1991), Wada et al (1991), Pendleton et al (1994), Chiar et al (2002), Mennella et al (2003), Moultaka et al (2004).…”

Section: Introductionmentioning

confidence: 84%

“…In addition, intrinsic extinction and reddening associated with individual stars are thought to occur as well in the central parsec (Blum et al 1996;Clénet et al 2001;Moultaka et al 2004). Moreover, ISO observations have shown deep absorption features in the MIR (Lutz et al 1996) in the direction of the Galactic Center.…”

Section: Introductionmentioning

confidence: 99%

VLTL-band mapping of the Galactic center IRS 3-IRS 13 region

Moultaka¹,

Eckart²,

Schödel³

et al. 2005

A&A

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This paper presents L-band ISAAC and NAOS/CONICA (VLT) spectroscopic observations of the IRS 3-IRS 13 Galactic Center region. The ISAAC data allowed us to build the first spectroscopic data cube of the region in the L-band domain. Using the L-band spectrum of the extinction along the line of sight towards the GC derived in a previous paper (Moultaka et al. 2004, A&A, 425, 529), it was also possible to correct the cube for the foreground extinction. Maps of the water ice and hydrocarbon absorption line strength were then derived. These maps are important diagnostics of the interstellar and circumstellar medium because water ices are observed in molecular clouds while hydrocarbons are usually good tracers of the diffuse ISM. These maps support our previous results that the absorption features most probably occur in the local Galactic center medium and can be associated with the individual sources. Moreover, turbulence seems to affect the studied region of the minispiral, which appears like a mixture of a dense and diffuse medium. Comparison of the concentrations of ice and hydrocarbon absorptions around IRS 13E, IRS 6E, and IRS 2, with similar concentrations at the location of the extended continuum emission around IRS 3, suggests that these sources might present outflows interacting with the surrounding ISM. It was also possible to derive Brα and Pfγ emission line maps. The results suggest that the physical conditions of the ISM are not uniform in the observed region of the minispiral especially at the edges of the minicavity. The emission line maps allowed us to find three sources with broad lines corresponding to an FWHM deconvolved line width of about 1100 km s −1 and moving towards us with a radial velocity of about −300 km s −1 . These sources are most probably new Wolf-Rayet type stars located in projection to the north and west of IRS 3. Their derived radial velocities and proper motions show that only two of them might belong to the two rotating disks of young stars reported by Genzel et al. (2003, ApJ, 594, 812) and Levin & Beloborodov (2003, ApJ, 590, L33). Previously, NAOS/CONICA (NACO) data allowed us to resolve the IRS13E3 region into two components E3N, and E3c (Eckart et al. 2004, ApJ, 602, 760). The new spectroscopic NACO data show that E3c is a good candidate for a Wolf-Rayet type star. In addition, three sources (η, ζ, and γ) out of the eight very red sources located in the IRS13N complex also presented in Eckart et al. (2004, ApJ, 602, 760) have been resolved spectroscopically with NACO. The spectra presented in this paper show that the red colors of the sources are probably due to extended dust emission.

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“…The spatially resolved intrinsic polarization patterns of both bright extended sources in our FOV do not show a centrosymmetric shape as would be expected for Mie scattering on spherical grains. Instead, the pattern found for IRS 1W suggests that scattering on aligned elongated grains must play a significant role, possibly combined with thermal dust emission (in the Ks-band), because the grains in the bowshocks may reach temperatures on the order of 1000 K (see Moultaka et al 2004). Both effects would produce polarization parallel to the long axis of the grains and thus perpendicular to their angular momentum.…”

Section: Discussionmentioning

confidence: 99%

Adaptive-optics assisted near-infrared polarization measurements of sources in the Galactic center

Witzel

Schödel

Eckart

et al. 2011

A&A

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Context. The Galactic center offers unique opportunities to study stellar and bow-shock polarization effects in a dusty environment. Aims. The goals of this work are to provide near-infrared (NIR) polarimetry of the stellar sources in the central parsec at the resolution of an 8 m telescope for the first time, along with new insights into the nature of the known bright bow-shock sources. Methods. We use adaptive-optics assisted observations obtained at the ESO VLT in the H-and Ks-band, applying both high-precision photometric methods specifically developed for crowded fields and a newly established polarimetric calibration for NACO to produce polarization maps of the central 3 × 19 , in addition to spatially resolved polarimetry and a flux variability analysis on the extended sources in this region. Results. We find foreground polarization mainly parallel to the Galactic plane, with average values of (4.6 ± 0.6)% at 26 • ± 6 • (Ks-band) and (9.3 ± 1.3)% at 20 • ± 6 • (H-band) in the center of the field-of-view (FOV). Farther away from the center, we find higher polarization degrees and steeper polarization angles: (7.5 ± 1.0)% at 11 • ± 6 • (Ks-band) and (12.1 ± 2.1)% at 13 • ± 6 • (H-band). p H /p Ks peaks at 1.9 ± 0.4, corresponding to a power law index for the wavelength dependency of α = 2.4 ± 0.7. These values also vary over the FOV, with higher values in the center. This is indicative of the influence of local effects on the total polarization, possibly dichroic extinction by Northern Arm dust. The two extended sources IRS 21 and 1W show similar intrinsic polarization degrees of 6.1 resp. 7.8% (Ks) and 6.9 (H, only 1W) at polarization angles coincident with previous NIR and mid-infrared (MIR) findings, both in total and spatially resolved. The spatial polarization pattern of both sources points to scattering on aligned elongated dust grains as the major source of intrinsic polarization, and matches the known orientation of the magnetic field. Our data also allow us to separate the bow shock of IRS 21 from the central source for the first time in the Ks-band, finding the apex north of the central source and determining a standoff distance of ∼400 AU, which matches previous estimates. This source also shows a ∼50% increase in flux in the NIR over several years.

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Dust embedded sources at the Galactic Center

Cited by 45 publications

References 102 publications

Ks- andLp-band polarimetry on stellar and bow-shock sources in the Galactic center

Ks- andLp-band polarimetry on stellar and bow-shock sources in the Galactic center

VLTL-band mapping of the Galactic center IRS 3-IRS 13 region

Adaptive-optics assisted near-infrared polarization measurements of sources in the Galactic center

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