DETERMINING THE DISTANCE OF LOOP I STRUCTURE AT SOUTHERN GALACTIC LATITUDE
Ilham Maulana (1) & Lucky Puspitarini (2*)

1) Bosscha Observatory, Faculty of Mathematics and Natural Sciences (FMIPA), Institut Teknologi Bandung, Jl. Peneropongan Bintang No. 45, Lembang 40391, Indonesia
2) Astronomy Research Division and Bosscha Observatory, FMIPA ITB, Jalan Ganesha 10, Bandung
40132, Indonesia


*Email: lucky.puspitarini[at]as.itb.ac.id

Abstract

Interstellar matter plays an important role in our Galaxy. It is an ingredient to form stars, but it can also change the apparent properties of stars and other astronomical objects. Therefore, it is important to understand the distribution of the ISM in the Galaxy. Although ISM is concentrated within the galactic disk, at high galactic latitude, we can also find a smaller amount of ISM as part of shell-like structures which are known as ^loop^. Efforts to determine the distance of the loop structures have been carried out, but mostly for the North Galactic Spur or North Polar Spur (NPS). The distance of these structures is under debate: is it a local or distant Galactic structure? In this work, we aim at determining the distance of Loop I structure at the southern galactic latitude by using high-resolution spectroscopic data from ESO-HARPS and stellar parallaxes from GAIA EDR3. The interstellar tracers are NaI and CaII lines which are recorded in the reddened stellar spectra. Stellar parallaxes of the target stars are used to constrain the distance of the ISM. Our results favor that the Loop I is a local structure (around 80 pc from the Sun).

Keywords: interstellar matter (ISM), Loop I, NPS, southern galactic latitude, spectroscopy

Topic: EARTH, ATMOSPHERIC, AND SPACE SCIENCE