scholarly journals Interstellar Extinction and Elemental Abundances: Individual Sight Lines

2021 ◽  
Vol 257 (2) ◽  
pp. 63
Author(s):  
Wenbo Zuo ◽  
Aigen Li ◽  
Gang Zhao
Keyword(s):  
Gas Phase ◽  
Interstellar Extinction ◽  
Elemental Abundance ◽  
Extinction Curve ◽  
Galactic Chemical Evolution ◽  
Space Telescopes ◽  
Dust Extinction ◽  
Elemental Abundances ◽  
Hydrogen Column Density ◽  
The Relationship

Abstract While it is well recognized that both the Galactic interstellar extinction curves and the gas-phase abundances of dust-forming elements exhibit considerable variations from one sight line to another, as yet most of the dust extinction modeling efforts have been directed to the Galactic average extinction curve, which is obtained by averaging over many clouds of different gas and dust properties. Therefore, any details concerning the relationship between the dust properties and the interstellar environments are lost. Here we utilize the wealth of extinction and elemental abundance data obtained by space telescopes and explore the dust properties of a large number of individual sight lines. We model the observed extinction curve of each sight line and derive the abundances of the major dust-forming elements (i.e., C, O, Si, Mg, and Fe) required to be tied up in dust (i.e., dust depletion). We then confront the derived dust depletions with the observed gas-phase abundances of these elements and investigate the environmental effects on the dust properties and elemental depletions. It is found that for the majority of the sight lines the interstellar oxygen atoms are fully accommodated by gas and dust and therefore there does not appear to be a “missing oxygen” problem. For those sight lines with an extinction-to-hydrogen column density A V /N H ≳ 4.8 × 10−22 mag cm2 H−1 there are shortages of C, Si, Mg, and Fe elements for making dust to account for the observed extinction, even if the interstellar C/H, Si/H, Mg/H, and Fe/H abundances are assumed to be protosolar abundances augmented by Galactic chemical evolution.

scholarly journals Central molecular zones in galaxies: 12CO-to-13CO ratios, carbon budget, and X factors

2020 ◽  
Vol 635 ◽  
pp. A131 ◽  
Author(s):  
F. P. Israel
Keyword(s):  
Gas Phase ◽  
Gas Content ◽  
Molecular Gas ◽  
Nearby Galaxy ◽  
Individual Values ◽  
Elemental Abundances ◽  
Hydrogen Column Density ◽  
Galaxy Center ◽  
The Mean ◽  
Co Emission

We present ground-based measurements of 126 nearby galaxy centers in 12CO and 92 in 13CO in various low-J transitions. More than 60 galaxies were measured in at least four lines. The average relative intensities of the first four J 12CO transitions are 1.00:0.92:0.70:0.57. In the first three J transitions, the average 12CO-to-13CO intensity ratios are 13.0, 11.6, and 12.8, with individual values in any transition ranging from 5 to 25. The sizes of central CO concentrations are well defined in maps, but poorly determined by multi-aperture photometry. On average, the J = 1−0 12CO fluxes increase linearly with the size of the observing beam. CO emission covers only a quarter of the HI galaxy disks. Using radiative transfer models (RADEX), we derived model gas parameters. The assumed carbon elemental abundances and carbon gas depletion onto dust are the main causes of uncertainty. The new CO data and published [CI] and [CII] data imply that CO, C°, and C+ each represent about one-third of the gas-phase carbon in the molecular interstellar medium. The mean beam-averaged molecular hydrogen column density is N(H2) = (1.5 ± 0.2)×1021 cm−2. Galaxy center CO-to-H2 conversion factors are typically ten times lower than the “standard” Milky Way X° disk value, with a mean X(CO) = (1.9 ± 0.2)×1019 cm−2/K km s−1 and a dispersion 1.7. The corresponding [CI]-H2 factor is five times higher than X(CO), with X[CI] = (9 ± 2)×1019 cm−2/K km s−1. No unique conversion factor can be determined for [CII]. The low molecular gas content of galaxy centers relative to their CO intensities is explained in roughly equal parts by high central gas-phase carbon abundances, elevated gas temperatures, and large gas velocity dispersions relative to the corresponding values in galaxy disks.

scholarly journals Probing the missing link between the diffuse interstellar bands and the total-to-selective extinction ratio $R_V\,\!-\!$ I. Extinction versus reddening

2019 ◽  
Vol 489 (1) ◽  
pp. 708-713 ◽  
Author(s):  
Kaijun Li ◽  
Aigen Li ◽  
F Y Xiang
Keyword(s):  
Extinction Ratio ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Interstellar Clouds ◽  
Diffuse Interstellar Bands ◽  
Hydrogen Column Density ◽  
Wide Range ◽  
Chemical Conditions ◽  
Physical And Chemical ◽  
Selective Extinction

ABSTRACT The carriers of the still (mostly) unidentified diffuse interstellar bands (DIBs) have been a long-standing mystery ever since their first discovery exactly 100 yr ago. In recent years, the ubiquitous detection of a large number of DIBs in a wide range of Galactic and extragalactic environments has led to renewed interest in connecting the occurrence and properties of DIBs to the physical and chemical conditions of the interstellar clouds, with particular attention paid to whether the DIB strength is related to the shape of the interstellar extinction curve. To shed light on the nature and origin of the DIB carriers, we investigate the relation between the DIB strength and RV, the total-to-selective extinction ratio, which characterizes how the extinction varies with wavelength (i.e. the shape of the extinction curve). We find that the DIB strength and RV are not related if we represent the strength of a DIB by its reddening-normalized equivalent width (EW), in contrast to the earlier finding of an anticorrelation in which the DIB strength is measured by the extinction-normalized EW. This raises a fundamental question about the appropriate normalization for the DIB EW. We argue that the hydrogen column density is a more appropriate normalization than extinction and reddening.

scholarly journals Impact of Hypernova νp-process Nucleosynthesis on the Galactic Chemical Evolution of Mo and Ru

2022 ◽  
Vol 924 (1) ◽  
pp. 29
Author(s):  
Hirokazu Sasaki ◽  
Yuta Yamazaki ◽  
Toshitaka Kajino ◽  
Motohiko Kusakabe ◽  
Takehito Hayakawa ◽  
...  
Keyword(s):  
Theoretical Prediction ◽  
Observational Data ◽  
Chemical Evolution ◽  
Elemental Abundance ◽  
Core Collapse ◽  
Galactic Chemical Evolution ◽  
Main Contributor ◽  
Elemental Abundances ◽  
The Galaxy ◽  
Low Metallicity

Abstract We calculate the Galactic Chemical Evolution of Mo and Ru by taking into account the contribution from ν p-process nucleosynthesis. We estimate yields of p-nuclei such as 92,94Mo and 96,98Ru through the ν p-process in various supernova progenitors based upon recent models. In particular, the ν p-process in energetic hypernovae produces a large amount of p-nuclei compared to the yield in ordinary core-collapse SNe. Because of this, the abundances of 92,94Mo and 96,98Ru in the Galaxy are significantly enhanced at [Fe/H] = 0 by the ν p-process. We find that the ν p-process in hypernovae is the main contributor to the elemental abundance of 92Mo at low metallicity [Fe/H] < −2. Our theoretical prediction of the elemental abundances in metal-poor stars becomes more consistent with observational data when the ν p-process in hypernovae is taken into account.

Contribution of Pahs to the Interstellar Extinction Curve

1992 ◽  
pp. 21-22 ◽  
Author(s):  
C. Joblin ◽  
A. Leger ◽  
P. Martin ◽  
D. Defourneau
Keyword(s):  
Interstellar Extinction ◽  
Extinction Curve

scholarly journals The interstellar extinction curve from 4000 Å to 6500 Å

1970 ◽  
Vol 36 ◽  
pp. 52-56
Author(s):  
G. A. H. Walker ◽  
J. B. Hutchings ◽  
P. F. Younger
Keyword(s):  
Interstellar Extinction ◽  
Absorption Peak ◽  
Extinction Curve ◽  
Linear Section ◽  
Broad Absorption ◽  
Diffuse Interstellar Bands

Interstellar extinction curves (mext vs. 1/λ) of 20 Å resolution have been obtained at the DAO from photoelectric scanner observations in the range 4000 Å to 5000 Å for five stars, and of 50 Å resolution for four stars in the range 4000 Å to 6500 Å from Willstrop's photoelectric data. There is a closely linear section between 4900 Å and 5800 Å for all of the curves. There are changes of gradient or discontinuities associated with the broadest diffuse interstellar bands at 6180 Å, 4882 Å, 4761 Å and 4430 Å. There is a marked discontinuity near 5800 Å and for some stars a broad absorption near 4200 Å. The 4430 Å band lies between two unequal wings of anomalously low extinction (one of which has been detected at Edinburgh). The irregularities vary from star to star, and those in the neighbourhood of the 4430 Å band seem to have the same form as those in the region of the absorption peak at 2200 Å

The ultraviolet interstellar extinction curve in the Pleiades

1981 ◽  
Vol 244 ◽  
pp. 199 ◽  
Author(s):  
A. N. Witt ◽  
R. C. Bohlin ◽  
T. P. Stecher
Keyword(s):  
Interstellar Extinction ◽  
Extinction Curve

scholarly journals Carbon and oxygen in metal-poor halo stars

2019 ◽  
Vol 622 ◽  
pp. L4 ◽  
Author(s):  
A. M. Amarsi ◽  
P. E. Nissen ◽  
M. Asplund ◽  
K. Lind ◽  
P. S. Barklem
Keyword(s):  
Chemical Evolution ◽  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Galactic Chemical Evolution ◽  
Elemental Abundances ◽  
Halo Stars ◽  
Effective Temperatures ◽  
Population Iii Stars ◽  
Hydrodynamic Effects ◽  
First Time

Carbon and oxygen are key tracers of the Galactic chemical evolution; in particular, a reported upturn in [C/O] towards decreasing [O/H] in metal-poor halo stars could be a signature of nucleosynthesis by massive Population III stars. We reanalyse carbon, oxygen, and iron abundances in 39 metal-poor turn-off stars. For the first time, we take into account 3D hydrodynamic effects together with departures from local thermodynamic equilibrium (LTE) when determining both the stellar parameters and the elemental abundances, by deriving effective temperatures from 3D non-LTE Hβ profiles, surface gravities from Gaia parallaxes, iron abundances from 3D LTE Fe II equivalent widths, and carbon and oxygen abundances from 3D non-LTE C I and O I equivalent widths. We find that [C/Fe] stays flat with [Fe/H], whereas [O/Fe] increases linearly up to 0.75 dex with decreasing [Fe/H] down to −3.0 dex. Therefore [C/O] monotonically decreases towards decreasing [C/H], in contrast to previous findings, mainly because the non-LTE effects for O I at low [Fe/H] are weaker with our improved calculations.

scholarly journals Depletion of 15N in the center of L1544: Early transition from atomic to molecular nitrogen?

2018 ◽  
Vol 615 ◽  
pp. L16 ◽  
Author(s):  
K. Furuya ◽  
Y. Watanabe ◽  
T. Sakai ◽  
Y. Aikawa ◽  
S. Yamamoto
Keyword(s):  
Gas Phase ◽  
Molecular Nitrogen ◽  
Abundance Ratio ◽  
Elemental Abundance ◽  
Evolutionary Stage ◽  
Gas Phase Chemistry ◽  
Far Ultraviolet ◽  
Phase Chemistry ◽  
Grain Surface

We performed sensitive observations of the N15ND+(1–0) and 15NND+(1–0) lines toward the prestellar core L1544 using the IRAM 30 m telescope. The lines are not detected down to 3σ levels in 0.2 km s−1 channels of ~6 mK. The non-detection provides the lower limit of the 14N/15N ratio for N2D+ of ~700–800, which is much higher than the elemental abundance ratio in the local interstellar medium of ~200–300. The result indicates that N2 is depleted in 15N in the central part of L1544, because N2D+ preferentially traces the cold dense gas, and because it is a daughter molecule of N2. In situ chemistry is probably not responsible for the 15N depletion in N2; neither low-temperature gas phase chemistry nor isotope selective photodissociation of N2 explains the 15N depletion; the former prefers transferring 15N to N2, while the latter requires the penetration of interstellar far-ultraviolet (FUV) photons into the core center. The most likely explanation is that 15N is preferentially partitioned into ices compared to 14N via the combination of isotope selective photodissociation of N2 and grain surface chemistry in the parent cloud of L1544 or in the outer regions of L1544, which are not fully shielded from the interstellar FUV radiation. The mechanism is most efficient at the chemical transition from atomic to molecular nitrogen. In other words, our result suggests that the gas in the central part of L1544 has previously gone trough the transition from atomic to molecular nitrogen in the earlier evolutionary stage, and that N2 is currently the primary form of gas-phase nitrogen.

scholarly journals How much graphene in space?

2019 ◽  
Vol 490 (3) ◽  
pp. 3875-3881 ◽  
Author(s):  
Qi Li ◽  
Aigen Li ◽  
B W Jiang
Keyword(s):  
Energy Range ◽  
Interband Transition ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Previous Estimate ◽  
Upper Limit ◽  
Vibrational Bands ◽  
Ir Emission ◽  
Electron Energy Loss ◽  
Planar Graphene

ABSTRACT The possible presence of graphene in the interstellar medium (ISM) is examined by comparing the interstellar extinction curve with the ultraviolet absorption of graphene calculated from its dielectric functions experimentally obtained with the electron energy loss spectroscopy (EELS) method. Based on the absence in the interstellar extinction curve of the $\sim \! 2755\, {\rm \mathring{\rm A} }$ π–π* electronic interband transition of graphene, we place an upper limit of $\sim \! 20\, {\rm ppm}$ of C/H on the interstellar graphene abundance, exceeding the previous estimate by a factor of $\sim \,$3 which made use of the dielectric functions measured with the spectroscopic ellipsometry (SE) method. Compared with the SE method which measures graphene in air (and hence its surface is contaminated) in a limited energy range of $\sim \,$0.7–5 $\, {\rm eV}$, the EELS probes a much wider energy range of $\sim \,$0–50 $\, {\rm eV}$ and is free of contamination. The fact that the EELS dielectric functions are substantially smaller than that of SE naturally explains why a higher upper limit on the graphene abundance is derived with EELS. Inspired by the possible detection of C24, a planar graphene sheet, in several Galactic and extragalactic planetary nebulae, we also examine the possible presence of C24 in the diffuse ISM by comparing the model IR emission of C24 with the observed IR emission of the Galactic cirrus and the diffuse ISM towards l = 44°20′ and b = −0°20′. An upper limit of $\sim \!20\, {\rm ppm}$ on C24 is also derived from the absence of the characteristic vibrational bands of C24 at $\sim \,$6.6, 9.8, and 20 $\, {\rm \mu m}$ in the observed IR emission.

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