An in-depth analysis of the RZ Piscium atmosphere

Abstract

The star RZ Psc is one of the most unusual members of the UX Ori star family. It demonstrates all properties that are typical of these stars (the light variability, high linear polarization in deep minima, the blueing effect), but until recently there has been no obvious evidence of its youth. Recently, we have shown that RZ Psc is in the transitional evolutionary stage between stars with the primordial and debris disks. In this paper we present the results of the quantitative analysis of the star's spectrum. Using the high-resolution (R = 46 000) spectrum of RZ Psc obtained with Nordic Optical Telescope, we determined T eff = 5350 ± 150 K, log g = 4.2 ± 0.2, [M/H] = −0.3 ± 0.05. These parameters agree well with the same ones as for the stars recently passed the T Tauri star evolutionary stage. This supports our previous suggestion about the evolutionary status of RZ Psc as the post-T Tauri and post-UX Ori star.

The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc

“…To circumvent this issue, we used just the 2 μm all-sky survey (2MASS [ 93 ]) and GALEX photometry, fitting a PHOENIX atmosphere model [ 94 ], finding a best-fit effective temperature of 5485 K (assuming no reddening, or 5600 K if some reddening is allowed to improve the fit slightly). These temperatures are consistent with that derived from a high-resolution spectrum; 5350±150 K [ 45 ]. Alternatively, fixing the temperature to the spectroscopic value yields a mild UV excess, less than a factor of two, that may be chromospheric.…”

“…Corroborating evidence comes from approximately 500 K temperature of the dust seen in the mid-IR, which places it near 0.4–0.7 AU (depending on optical depth) and therefore at a location consistent with the occulting dust [ 40 ]. The distance to RZ Psc is unknown, but as an apparently isolated star that shows Li absorption the age has been estimated as a few tens of Myr, and therefore beyond the age at which a gas-rich disc would normally exist [ 39 , 45 ]. Further distinguishing features are that the duration of the dimming events is consistently short compared with other UXors, a few days rather than days to a few weeks, and that no near-IR (i.e.…”

“…Further distinguishing features are that the duration of the dimming events is consistently short compared with other UXors, a few days rather than days to a few weeks, and that no near-IR (i.e. K-band) excess or accretion signatures are seen [ 45 ], so interpretations related to accretion of disc material onto the star [ 21 , 30 , 34 ] are unlikely.…”

“…In figure 8 , we have converted the gradients into semi-major axes using equation ( 4.7 ). The dashed line shows the stellar radius, estimated to be approximately solar based on an age of 25 Myr [ 71 ] and an effective temperature of 5350 K [ 45 ], using Siess et al’s [ 72 ] isochrones. Figure 8 also includes solid lines of constant gradient, computed using equation ( 4.7 ) and f min =1− τ .…”

“…has an inner hole), it does not preclude the possibility that gas resides in that hole and may still be accreting onto the star. No emission lines that would provide evidence of accretion have been seen [45,73], but as a further test we reconsidered the spectral energy distribution. Specifically, we included photometry from the galaxy evolution explorer (GALEX [91]) to quantify the level of any ultraviolet (UV) excess, a complementary accretion indicator [92].…”