Stellar Photospheric Contamination: Evolution from Protoplanetary to Debris Disks

Stellar Photospheric Contamination: Evolution from Protoplanetary to Debris Disks S. Borthakur1,3(sandipan.bor[email protected]), M. Kama2,1, L. Fossati3, Q. Kral4, C. P. Folsom1, J. Teske5, A. Aret1 1Tartu Observatory, Estonia; 2University College London, UK; 3Space Research Institute, Austria; 4LESIA, Observatoire de Paris, CNRS, France; 5Earth and Planets Laboratory, Carnegie Institution for Science, USA Digital Version Motivation Stellar abundances depleted in refractory elements are observed in some debris disk-hosting A-type stars, likely tracing accretion from their earlier protoplanetary disk (PPD) stage. Accretion from protoplanetary disks contaminates the stellar photosphere. Stars hotter than 6250 K show clear contamination signatures due to slower mixing than cooler stars[1]. Giant planet formation opens gaps in PPDs, forming dust traps at the outer edge due to pressure bumps. This leads to dust-poor accretion and refractory depleted abundance measurements in the stellar photosphere[2]. This contamination signature remains for a timescale equal to the accretion timescale (∼10 Myr). This study measures the stellar abundance of six A-type stars hosting debris disks (DD), where low accretion rates suggest no contamination from debris disk material. Stellar photospheric abundance evolution Stellar photospheres are contaminated by accretion from PPDs. During the DD stage, accretion rates are too low for any visible signatures. The stellar abundances eventually revert to pre-contamination levels due to photospheric mixing. Fig.1. Evolutionary tracks of refractory elements at the stellar photosphere of - group I PPD (GI, with gaps) hosting stars, and group II PPD (GII, no gaps) hosting stars[2]. DD sample - our DD star analysis, DD S21 - Saffe, 2021[3] Fig.2. Constant volatile abundances as dust traps don’t affect gas accretion. Contamination Equation fph(˙ M, νrot)- Contamination fraction calculated using stellar mixing model, CAMStars[4] ˙ Maccretion rate of the disk on the star νrot - rotational velocity of the star Different ˙ Mof HD 110058 • HD 110058 is a DD hosting star with current ˙ M≈10−13M⊙/yr [5] and calculated fph ≈0[4]. • To explain the observed (Fe/H)obs, we need a minimum ˙ M≈10−7M⊙/yr, which is five orders of magnitude higher than the current value (Fig. 3) and comparable to accretion rates of protoplanetary disks. The difference in the current and inferred accretion rates of HD 110058 supports the idea that refractory depletion in some young DD-hosting hot stars stems from prior protoplanetary disk accretion. Fig.3. Range of fph,˙ Mand (X/H)acc satisfying eq.1 for HD 110058. Black dots represent a sample of PPD hosting hot stars. Summary and Outlook • Studying photospheric contamination can provide evidence of giant planet formation, which sometimes remains elusive to direct detection. • Debris disk hosting stars can still have refractory depleted abundances, indicating contamination signature from its protoplanetary disk stage. • Hint of a separate population of stars with more substantial refractory depletion than others. The reason for this is still not clear. References 1. Folsom C. P. et al. 2012, MNRAS, 422, 2072. 2. Kama M., Folsom C. P., Pinilla P., 2015, A&A, 582, L10. 3. Saffe C. et al., 2021, A&A, 647, A49. 4. Jermyn A. S., Kama M., 2018, MNRAS, 476, 4418. 5. Kral Q., Matrà L., Wyatt M. C., Kennedy G. M., 2017, MNRAS, 469, 521. Acknowledgement