GK Car and GZ Nor: Two low-luminous, depleted RV Tauri stars

• Main Authors: Gezer, I, Van Winckel, H, Manick, R, Kamath, D
• Format: Journal Article
• Language: English
• Published: 18-07-2019
• Subjects: Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.1907.07937

Proc. IAU 14 (2018) 404-405 We performed a photometric and spectroscopic analysis of two RV Tauri stars
GK Car and GZ Nor. Both objects are surrounded by hot circumstellar dust. Their
pulsation periods, derived from ASAS photometric time series, have been used to
derive their luminosities and distances via the PLC relation. In addition, for
both objects, GAIA distances are available. The Gaia distances and luminosities
are consistent with the values obtained from the PLC relationship. GK Car is at
distance of 4.5$\pm{1.3}$ kpc and has a luminosity of 1520$\pm{840}$
L$_{\odot}$, while GZ Nor is at distance of 8.4$\pm{2.3}$ kpc and has a
luminosity of 1240 $\pm{690}$ L$_{\odot}$. Our abundance analysis reveals that
both stars show depletion of refractory elements with [Fe/H]=$-$1.3 and
[Zn/Ti]=$+$1.2 for GK Car and [Fe/H]=$-$2.0 and [Zn/Ti]=$+$0.8 for GZ Nor. In
the WISE colour-colour diagram, GK Car is located in the RV Tauri box as
originally defined by \cite{evans85} and updated by \cite{gezer15}, while GZ
Nor is not. Despite this, we argue that both objects are surrounded by a
gravitationally bound disc. As depletion is observed in binaries, we postulate
that both stars are binaries as well. RV Tauri stars are generally acknowledged
to be post$-$AGB stars. Recent studies show that they might be either indeed
post$-$AGB or post$-$RGB objects depending on their luminosity. For both
objects, the derived luminosities are relatively low for post-AGB objects,
however, the uncertainties are quite large. We conclude that they could be
either post-RGB or post-AGB objects.