# Optical spectrum of distant OH/IR star V1648 Aql (IRAS 19386+0155)

## TL;DR

This study presents a detailed optical spectral analysis of the distant post-AGB star V1648 Aql, revealing its radial velocities, interstellar features, and atmospheric parameters, confirming its evolutionary status.

## Contribution

The paper provides the first high-resolution optical spectrum of V1648 Aql and determines its fundamental parameters and chemical abundances, confirming its classification as a post-AGB star.

## Key findings

- Radial velocity V_r=10.18 km/s from metallic lines.
- Interstellar NaI and DIBs velocities match, indicating interstellar origin.
- Estimated luminosity M_V≈-5 and distance ≥1.8 kpc.

## Abstract

An optical spectrum of the star V1648 Aql (=IRAS 19386+0155) was obtained at the 6-meter telescope with a spectral resolution of R$\ge$60\,000. Heliocentric radial velocity measured from numerous metallic absorptions is equal to V$_r$=$10.18\pm0.05$ km s$^{-1}$ (V$_{\rm LSR}$=18.1 km s$^{-1}$). We determined the atmospheric, circumstellar, and interstellar components in the profile of the NaI D~lines at V$_r$=9.2, $-3.4$, and $-12.8$ km s$^{-1}$ respectively. The averaged over twenty identified DIBs velocity V$_r$(DIBs)=$-12.5\pm0.2$ km~s$^{-1}$ coincides with the interstellar NaI component. Weak emissions with an intensity of about 10% of the local continuum level were detected in the spectrum; they are identified as low-excitation metal lines. Their averaged position, V$_r$=$8.44\pm0.28$ km s$^{-1}$, may point to the presence of a weak velocity gradient in the upper layers of the stellar atmosphere. Based on the spectroscopic data and taking into account the interstellar and circumstellar reddening, we estimated the star's luminosity M$_V\approx-5^{\rm m}$ and also obtained the lower estimate of distance d$\ge1.8$ kpc. Using the model atmosphere method, we determined the fundamental parameters and chemical abundances in the atmosphere approving the status of a post-AGB star for V1648 Aql.