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Register a new userNear infrared diffuse interstellar bands toward the Cygnus OB2 association
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We obtained the near-infrared (NIR) high-resolution ($Requivlambda/Deltalambdasim20,000$) spectra of the seven brightest early-type stars in the Cygnus OB2 association for investigating the environmental dependence of diffuse interstellar bands (DIBs). The WINERED spectrograph mounted on the Araki 1.3m telescope in Japan was used to collect data. All 20 of the known DIBs within the wavelength coverage of WINERED ($0.91<lambda<1.36mu$m) were clearly detected along all lines of sight because of their high flux density in the NIR wavelength range and the large extinction. The equivalent widths (EWs) of DIBs were not correlated with the column densities of C$_2$ molecules, which trace the patchy dense component, suggesting that the NIR DIB carriers are distributed mainly in the diffuse component. On the basis of the correlations among the NIR DIBs both for stars in Cyg OB2 and stars observed previously, $lambdalambda$10780, 10792, 11797, 12623, and 13175 are found to constitute a family, in which the DIBs are correlated well over the wide EW range. In contrast, the EW of $lambda$10504 is found to remain almost constant over the stars in Cyg OB2. The extinction estimated from the average EW of $lambda$10504 ($A_Vsim3.6$mag) roughly corresponds to the lower limit of the extinction distribution of OB stars in Cyg OB2. This suggests that $lambda$10504 is absorbed only by the foreground clouds, implying that the carrier of $lambda$10504 is completely destroyed in Cyg OB2, probably by the strong UV radiation field. The different behaviors of the DIBs may be caused by different properties of the DIB carriers.
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We map the distribution and properties of the Milky Ways interstellar medium as traced by diffuse interstellar bands (DIBs) detected in near-infrared stellar spectra from the SDSS-III/APOGEE survey. Focusing exclusively on the strongest DIB in the H-band, at ~1.527 microns, we present a projected map of the DIB absorption field in the Galactic plane, using a set of about 60,000 sightlines that reach up to 15 kpc from the Sun and probe up to 30 magnitudes of visual extinction. The strength of this DIB is linearly correlated with dust reddening over three orders of magnitude in both DIB equivalent width (W_DIB) and extinction, with a power law index of 1.01 +/- 0.01, a mean relationship of W_DIB/A_V = 0.1 Angstrom mag^-1, and a dispersion of ~0.05 Angstrom mag^-1 at extinctions characteristic of the Galactic midplane. These properties establish this DIB as a powerful, independent probe of dust extinction over a wide range of A_V values. The subset of about 14,000 robustly detected DIB features have an exponential W_DIB distribution. We empirically determine the intrinsic rest wavelength of this transition to be lambda_0 = 15,272.42 Angstrom, and then calculate absolute radial velocities of the carrier, which display the kinematical signature of the rotating Galactic disk. We probe the DIB carrier distribution in three dimensions and show that it can be characterized by an exponential disk model with a scaleheight of about 100 pc and a scalelength of about 5 kpc. Finally, we show that the DIB distribution also traces large-scale Galactic structures, including the central long bar and the warp of the outer disk.
Discovered almost a century ago, the Diffuse Interstellar Bands (DIBs) still lack convincing and comprehensive identification. Hundreds of DIBs have now been observed in the near-ultraviolet (NUV), visible and near-infrared (NIR). They are widely held to be molecular in origin, and modelling of their band profiles offers powerful constraints on molecular constants. Herschel 36, the illuminating star of the Lagoon Nebula, has been shown to possess unusually broad and asymmetric DIB profiles in the visible, and is also bright enough for NIR observation. We present here high-resolution spectroscopic observations targeting the two best-known NIR DIBs at 11797.5 and 13175 A toward this object and a nearby comparison O-star, 9 Sgr, using the GNIRS instrument on Gemini North. We show a clear detection of the 13175 A DIB in both stars, and find (i) that it does not exhibit the unusual wing structure of some of the visual DIBs in Her 36 and (ii) that the depth of the band in the two objects is very similar, also contrary to the behaviour of the visual DIBs. We discuss the implications of these results for multiple DIB carrier candidates, and the location of their carriers along the observed lines of sight.
We present a large-scale study of diffuse X-ray emission in the nearby massive stellar association Cygnus OB2 as part of the Chandra Cygnus OB2 Legacy Program. We used 40 Chandra X-ray ACIS-I observations covering $sim$1.0 deg$^2$. After removing 7924 point-like sources detected in our survey, background-corrected X-ray emission, the adaptive smoothing reveals large-scale diffuse X-ray emission. Diffuse emission was detected in the sub-bands Soft [0.5 : 1.2] and Medium [1.2 : 2.5], and marginally in the Hard [2.5 : 7.0] keV band. From X-ray spectral analysis of stacked spectra we compute a total [0.5 : 7.0 keV] diffuse X-ray luminosity of L$_{rm x}^{rm diff}approx$4.2$times$10$^{rm 34}$ erg s$^{-1}$, characterized with plasma temperature components at kT$approx$ 0.11, 0.40 and 1.18 keV, respectively. The HI absorption column density corresponding to these temperatures has a distribution consistent with N$_{rm H}$ = 0.43, 0.80 and 1.39 $times$10$^{22}$ cm$^{-2}$. The extended medium band energy emission likely arises from O-type stellar winds thermalized by wind-wind collisions in the most populated regions of the association, while the soft band emission probably arises from less energetic termination shocks against the surrounding Interstellar-Medium. Super-soft and Soft diffuse emission appears more widely dispersed and intense than the medium band emission. The diffuse X-ray emission is generally spatially coincident with low-extinction regions that we attribute to the ubiquitous influence of powerful stellar winds from massive stars and their interaction with the local Interstellar-Medium. Diffuse X-ray emission is volume-filling, rather than edge-brightened, oppositely to other star-forming regions. We reveal the first observational evidence of X-ray haloes around some evolved massive stars.
The wavelength displacement of the Diffuse Interstellar Bands at 4502, 5705, 5780, 6284, and 7224 AA with respect to the well known, narrow atomic/molecular interstellar lines (of Ca{sc ii} and Na{sc i}) have been measured in the spectra of the 2 Orion Trapezium stars HD 37022 and HD 37020, using the HARPStextendash N spectrograph, fed with the 3.5 m Telescopio Nazionale Galileo, and the BOES spectrograph, fed with the 1.8m Korean telescope. The red shift is $sim$25 km/s for all these DIBs. We discuss the various possible origins of this very peculiar wavelength shift in the light of the particular physical conditions in the Orion Trapezium. The above mentioned shift is seemingly absent in the DIBs at 6196 and 6993 AA.
The spectrum of any star viewed through a sufficient quantity of diffuse interstellar material reveals a number of absorption features collectively called diffuse interstellar bands (DIBs). The first DIBs were reported 90 years ago, and currently well over 500 are known. None of them has been convincingly identified with any specific element or molecule, although recent studies suggest that the DIB carriers are polyatomic molecules containing carbon. Most of the DIBs currently known are at visible and very near-infrared wavelengths, with only two previously known at wavelengths beyond one micron (10,000 Angstroms), the longer of which is at 1.318 microns. Here we report the discovery of thirteen diffuse interstellar bands in the 1.5-1.8 micron interval on high extinction sightlines toward stars in the Galactic centre. We argue that they originate almost entirely in the Galactic Centre region, a considerably warmer and harsher environment than where DIBs have been observed previously. The relative strengths of these DIBs toward the Galactic Centre and the Cygnus OB2 diffuse cloud are consistent with their strengths scaling mainly with extinction by diffuse material.
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