# HD 44892: The youngest (or oldest?) gas-harbouring debris disc around an intermediate mass star

## TL;DR

This study reports the first detection of gas around a young intermediate-mass star with a debris disc, revealing insights into the transition from protoplanetary to debris disc stages and the gas dispersal timeline.

## Contribution

First detection of gas in a 2.1 Myr old debris disc around an intermediate-mass star, combining ALMA and UVES data to analyze gas and dust properties.

## Key findings

- Detected CO gas mass of approximately 7.86×10⁻⁵ to 1.62×10⁻⁴ M_⊕
- Identified variability in Ca II lines indicating circumstellar gas transits
- Estimated dust mass of 0.019±0.009 M_⊕, suggesting late gas dispersal stage

## Abstract

We present the first detections of gas around a 2.1 Myr old debris disc-bearing intermediate-mass star, HD 44892. Gas is detected both in $^{12}$CO (2-1) emission through ALMA Band 6 observations and in absorption in Ca II K and H, seen with high-resolution UVES spectroscopy. $^{13}$CO and C$^{18}$O (2-1) are not detected. The star exhibits a 12 $\mu$m fractional excess of $7.86^{+0.11}_{-2.27}$, placing it in the transition stage between protoplanetary and debris discs. Our detection of 1.3 mm emission yields the dust mass of 0.019$\pm$0.009 $M_{\oplus}$ assuming 115 K temperature. The $^{13}$CO non-detection places an upper limit on CO gas mass of $\sim$10$^{-2}$ $M_{\oplus}$. The $^{12}$CO detection yields a CO gas mass of (7.86$\pm$2.05)$\times$10$^{-5}$ $M_{\oplus}$ or (1.62$\pm$0.17)$\times$10$^{-4}$ $M_{\oplus}$ assuming a gas temperature of 20 K or 50 K, respectively. These should be considered as lower limits since $^{12}$CO emission may be optically thick. With UVES, we find variability in Ca II K and H lines, which can be interpreted by transiting circumstellar gas, ruling out interstellar absorption as their origin. Both the dust mass, which is within an order of magnitude of HD 141569, and the gas mass derived here indicate a late gas dispersal stage of the protoplanetary disc. Through our analysis we deem the alternative age of 800 Myr unlikely.