Context. The accretion luminosity (L-acc) in young, low-mass stars is crucial for understanding stellar formation. However, obtaining direct measurements is often hindered by limited spectral coverage and challenges in UV-excess modeling. Empirical relations linking L-acc to various accretion tracers are widely used to overcome these limitations. Aims. This work revisits these empirical relations using the PENELLOPE dataset, evaluating their applicability across different star-forming regions as well as accreting young objects other than Classical T Tauri Stars (CTTSs; Class II sources). Methods. We analyzed the PENELLOPE VLT/X-shooter dataset of 64 CTTSs, measuring fluxes of several accretion tracers and adopting the stellar and accretion parameters derived from studies based on PENELLOPE. For 61 sources, we supplemented our analysis with the ODYSSEUS HST data set, which covers a wider spectral range in NUV bands. Results. We compared the L-acc values obtained in the PENELLOPE and ODYSSEUS surveys, which employed a single hydrogen slab model (XS-fit) and a multi-column accretion shock model (HST-fit), respectively, and found statistically consistent results. Our analysis confirms that existing empirical relations, previously derived for the Lupus sample, provide reliable L-acc estimates for CTTSs in several other star-forming regions. We revisit empirical relations for accretion tracers in our dataset, based on HST-fit, with coefficients which are consistent within 1 sigma with XS-fit results for most lines. We also propose a method to estimate extinction using these relations and investigate the empirical relations for Brackett lines (Br8 to Br21). Conclusions. The L-acc - L-line empirical relations can be successfully used for statistical studies of accretion on young forming objects in different star-forming regions. These relations also offer a promising approach to independently estimate extinction in CTTSs, provided a sufficient number of flux-calibrated tracers are available across a broad spectral range. We confirm that near-infrared lines (Pa beta and Br gamma) serve as reliable tracers of L-acc in high accretors, making them valuable tools for probing accretion properties of high accreting young stars not accessible in the UVB.
Fiorellino, E., Alcalá, J.M., Manara, C.F., Pittman, C.V., Ábrahám, P., Venuti, L., et al. (2025). PENELLOPE: VII. Revisiting empirical relations to measure accretion luminosity. ASTRONOMY & ASTROPHYSICS, 704, 42-67 [10.1051/0004-6361/202556603].
PENELLOPE: VII. Revisiting empirical relations to measure accretion luminosity
Fiorellino E.
Primo
Writing – Original Draft Preparation
;Lodato G.;
2025
Abstract
Context. The accretion luminosity (L-acc) in young, low-mass stars is crucial for understanding stellar formation. However, obtaining direct measurements is often hindered by limited spectral coverage and challenges in UV-excess modeling. Empirical relations linking L-acc to various accretion tracers are widely used to overcome these limitations. Aims. This work revisits these empirical relations using the PENELLOPE dataset, evaluating their applicability across different star-forming regions as well as accreting young objects other than Classical T Tauri Stars (CTTSs; Class II sources). Methods. We analyzed the PENELLOPE VLT/X-shooter dataset of 64 CTTSs, measuring fluxes of several accretion tracers and adopting the stellar and accretion parameters derived from studies based on PENELLOPE. For 61 sources, we supplemented our analysis with the ODYSSEUS HST data set, which covers a wider spectral range in NUV bands. Results. We compared the L-acc values obtained in the PENELLOPE and ODYSSEUS surveys, which employed a single hydrogen slab model (XS-fit) and a multi-column accretion shock model (HST-fit), respectively, and found statistically consistent results. Our analysis confirms that existing empirical relations, previously derived for the Lupus sample, provide reliable L-acc estimates for CTTSs in several other star-forming regions. We revisit empirical relations for accretion tracers in our dataset, based on HST-fit, with coefficients which are consistent within 1 sigma with XS-fit results for most lines. We also propose a method to estimate extinction using these relations and investigate the empirical relations for Brackett lines (Br8 to Br21). Conclusions. The L-acc - L-line empirical relations can be successfully used for statistical studies of accretion on young forming objects in different star-forming regions. These relations also offer a promising approach to independently estimate extinction in CTTSs, provided a sufficient number of flux-calibrated tracers are available across a broad spectral range. We confirm that near-infrared lines (Pa beta and Br gamma) serve as reliable tracers of L-acc in high accretors, making them valuable tools for probing accretion properties of high accreting young stars not accessible in the UVB.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
