We report on the spectroscopic classification of a likely YSO observed with the MISTRAL spectrograph (http://www.obs-hp.fr/guide/mistral/MISTRAL_spectrograph_camera.shtml, Schmitt et al., 2024A&A...687A.198S) on the night of October 11th 2024 (AT2024xdo) at Observatoire de Haute Provence on the T193 telescope (http://www.obs-hp.fr/welcome.shtml and http://www.obs-hp.fr/guide/t193.shtml).
Observations were performed with the blue grism (4200-8200A) at a resolution of ~700, during 30min. Data were reduced with the ASPIRED MISTRAL-customized package (Lam et al., 2023AJ....166...13).
The counterpart of AT2024xdo (=Gaia24cts, 2024TNSTR3840....1H) is Gaia DR3 3315384559723861760, which is located based on Gaia EDR3 at a distance of 434 pc (421--447 pc, 68% confidence interval around the median; Bailer-Jones et al. 2021, AJ, 161, 3, 147). It was identified from Gaia DR2 using three dimensional density maps as a pre-main sequence (PMS) source of the Orion star-forming complex (Zari et al. 2018, A&A, 620, A172).
Using a preliminar data reduction of the best 15min exposure, the MISTRAL spectral continuum shows strong TiO absorption bands characteristic of M spectral-type. We determine from the TiO-7140 spectral index (Herczeg & Hillenbrand 2014, ApJ, 786, 97) a M3.6±0.3 spectral-type, hence this source is a low-mass star. The Halpha line emission is prominent, with EW=-129.6 A well above the chromospheric activity of the main-sequence dMe stars with the same spectral type (EW=-14 A; Martin et al. 1998, MNRAS, 300, 733), confirming the PMS status of this source.
The accretion criteria of 270 km/s for the full width at 10% of the Hα emission profile peak (FW10%Ha; White & Basri 2003) corresponds after convolution with MISTRAL line response to FWHM=9.00 A (Equation C.3 of Schmitt et al. 2024, A&A, 687, A198). Therefore, the observed FWHM(Ha)=9.07 A (corresponding to FW10%Ha=285.2 km/s) is a hint for accretion; however, the relative error of the MISTRAL line response is not modeled with 1% accuracy to firmly determine the accretion status of this T Tauri star.
The Gaia alert on 2024-09-30 00:43:59 (AT2024xdo; Hodgkin et al. 2024) was triggered by a rise in the G-band to 16.38 AB magnitude compared to the historic magnitude of 16.68 (0.02), which was followed 4.2h later by a decay of 0.05 AB magnitude in the G-band. This decay (if confirmed) would be consistent with a magnetic stellar flare rather than the (rare) onset of episodic accretion (see review by Audard et al. 2014, Protostars & Planets VI, 387-410, arXiv:1401.3368).
Photometry follow-ups of this target is encouraged to confirm the true behavior of this PMS low-mass star.
Catalog | Name | Reported RA | Reported DEC | Reported Obj-Type | Reported Redshift | Host Name | Host Redshift | Remarks | TNS RA | TNS DEC | TNS Obj-Type | TNS Redshift |
---|---|---|---|---|---|---|---|---|---|---|---|---|
TNS | 2024xdo | 06:08:19.860 | +02:14:17.77 | Other | 0 | 06:08:19.860 | +02:14:17.77 |