Mapping Local Interstellar Medium With Diffuse Interstellar Bands. (arXiv:2008.03278v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Piecka_M/0/1/0/all/0/1">Martin Piecka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Paunzen_E/0/1/0/all/0/1">Ernst Paunzen</a>
With the use of the data from archives, we studied the correlations between
the equivalent widths of four diffuse interstellar bands (4430$r{A}$,
5780$r{A}$, 5797$r{A}$, 6284$r{A}$) and properties of the target stars
(colour excess values, distances and Galactic coordinates). Many different
plots of the diffuse interstellar bands and their maps were produced and
further analysed. There appears to be a structure in the plot of equivalent
widths of 5780$r{A}$ DIB (and 6284$r{A}$ DIB) against the Galactic
$x$-coordinate. The structure is well defined below $sim150$ m$r{A}$ and
within $|x|<250$ pc, peaking around $x=170$ pc. We argue that the origin of
this structure is not a statistical fluctuation. Splitting the data in the
Galactic longitude into several subregions improves or lowers the well known
linear relation between the equivalent widths and the colour excess, which was
expected. However, some of the lines of sight display drastically different
behaviour. The region within $150^circ<l<200^circ$ shows scatter in the
correlation plots with the colour excess for all of the four bands with
correlation coefficients $textrm{R}<0.58$. We suspect that the variation of
physical conditions in the nearby molecular clouds could be responsible.
Finally, the area $250^circ<l<300^circ$ displays (from the statistical point
of view) significantly lower values of equivalent widths than the other regions
— this tells us that there is either a significant underabundance of carriers
(when compared with the other regions) or that this has to be a result of an
observational bias.
With the use of the data from archives, we studied the correlations between
the equivalent widths of four diffuse interstellar bands (4430$r{A}$,
5780$r{A}$, 5797$r{A}$, 6284$r{A}$) and properties of the target stars
(colour excess values, distances and Galactic coordinates). Many different
plots of the diffuse interstellar bands and their maps were produced and
further analysed. There appears to be a structure in the plot of equivalent
widths of 5780$r{A}$ DIB (and 6284$r{A}$ DIB) against the Galactic
$x$-coordinate. The structure is well defined below $sim150$ m$r{A}$ and
within $|x|<250$ pc, peaking around $x=170$ pc. We argue that the origin of
this structure is not a statistical fluctuation. Splitting the data in the
Galactic longitude into several subregions improves or lowers the well known
linear relation between the equivalent widths and the colour excess, which was
expected. However, some of the lines of sight display drastically different
behaviour. The region within $150^circ<l<200^circ$ shows scatter in the
correlation plots with the colour excess for all of the four bands with
correlation coefficients $textrm{R}<0.58$. We suspect that the variation of
physical conditions in the nearby molecular clouds could be responsible.
Finally, the area $250^circ<l<300^circ$ displays (from the statistical point
of view) significantly lower values of equivalent widths than the other regions
— this tells us that there is either a significant underabundance of carriers
(when compared with the other regions) or that this has to be a result of an
observational bias.
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