Study of vertical abundance stratiﬁcation of elements in the stellar atmosphere of HD 63401 P. Kashko¹, V. Khalack² ¹Faculty of Physics, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine ²Département de Physique et d’Astronomie, Université de Moncton, Moncton, N.B., Canada E1A 3E9 Abstract Results Chemical abundance References HD63401 is one of the magnetic chemically peculiar (mCP) stars that were recently observed by the space telescope TESS. It may possess a hydro- dynamically stable stellar atmosphere where atomic diﬀusion in combination with a magnetic ﬁeld can lead to vertical stratiﬁcation of elements abundances. The modiﬁed ZEEMAN2 code was employed to carry out an abundance analysis of high-resolution and high signal-to-noise spectra obtained for HD63401 with ESPaDOnS. We found that only iron shows clear evidence of vertical abundance stratiﬁcation in the stellar atmosphere of HD63401. Seven high-resolution spectra were acquired with the spectropolarimeter ESPaDOnS for HD63401. To reduce the obtained data the software package Libre-ESpRIT (Donati et al., 1997) was used. The estimates of the eﬀective temperature and surface gravity are obtained from the best ﬁt of Balmer line proﬁles observed in Stokes I spectra by the theoretical proﬁles with the help of FITSB2 code (Napiwotzki et al., 2004). The derived values of Teﬀ=13360 K and log(g)=4.1 were used to calculate a model of the stellar atmosphere employing the code PHOENIX (Hauschildt et al. 1997), which is required to carry out abundance analysis with the help of ZEEMAN2 code (Landstreet, 1988). To select line proﬁles suitable for analysis we used an automatic procedure developed by Khalack (2018). Fig. 1 presents an example of the FeII 5100A line proﬁle ﬁtted by ZEEMAN2 code. Figure 2. The vertical stratiﬁcation of iron in the atmosphere of HD63401. The red line is the best line ﬁt derived using Levenberg-Marquardt algorithm Table 1. Average chemical abundance of HD63401 derived from the analysis of ESPaDOnS. We have done spectral analysis of seven available spectra of HD 63401, provided by ESPaDOnS . We derived the averaged chemical abundance of 30 elements. Our estimates are in good accordance with the results published by Bailey et al. (2014), except for Mg, Fe and Pr. Using the Levenberg-Marquardt algorithm ﬁtting algorithm (Marquardt 1963) to the results of analysis of all seven spectra we detected a vertical stratiﬁcation of iron abundance in stellar atmosphere of HD63401. Bagnulo S., Landstreet J. D., Mason E., et al., 2006, A&A 450 (2), p. 777-791 Bailey J. D., Landstreet J. D., Bagnulo S., 2014, A&A 561, p. A147 Donati J. F., Semel M., Carter B. D., et al., 1997, MNRAS 291, p. 658 Hubrig S., North P., Schöller M., et al., 2006, Astron. Nachr. 327, p. 289-297 Hauschildt P. H., Shore S. N., Schwarz G. J., et al., 1997, ApJ 490, p. 803 Grevesse, N., Scott, P., Asplund, M., et al., 2015, A&A 573, p. A27 Kashko P., Khalack V., Kobzar O., et al., 2020, PTA Proc. 2020, accepted (arXiv:2003.02925) Khalack V., 2018, MNRAS 477, p. 882 Kochukhov O., Bagnulo S., 2006, A&A 450, p. 763 Landstreet J. D., 1988, ApJ 326, p. 967 Marquardt D. W., 1963, SIAM Journal on Applied Mathematics 11, p. 431 Napiwotzki, R., et al., 2004, Astronomical Society of the Paciﬁc Conference Series 318, p. 402–410 Figure 1. The line proﬁle of FeII, ﬁtting by theoretical proﬁle using ZEEMAN2 code We found the phases of spectra using the rotational period P=2.414±0.018 d, derived by Kashko et al. (2020). To check if chemical abundances have vertical stratiﬁcation in the atmosphere of HD63401 we have ﬁtted the chemical abundance estimates at diﬀerent optical depths by a line (y = a*x + b) using the Levenberg-Marquardt algorithm (Marquardt, 1963). It uses the method of least squares to ﬁnd the best ﬁt. We used Python and function curve_ﬁt from library scipy (optimize) for the implementation of the algorithm. To select a signiﬁcant stratiﬁcation of chemical abundances throughout all elemen