We discuss a revision of accretion activity and kinematics of the enigmatic isolated UX Ori type star RZ Psc. Previously, RZ Psc was known to possess only spectroscopic signatures of outflow in the ...low-excitation lines of alkali metals. The archival high-resolution spectra reveal a short-lived episode of magnetospheric accretion in the system observed via inverse P Cyg profiles at the Hα and Ca II 8542 Å lines. The simultaneous presence of accretion and outflow signatures at Ca II 8542 Å is suggestive of an accretion-driven origin of the RZ Psc wind. We argue that RZ Psc experiences matter ejection via the magnetic propeller mechanism but variable accretion episodes allow it to sometimes move in the magnetospheric accretion regime. The presence of the weak accretion in the system is also supported by the radiation of the hot accretion spot on the stellar surface observed spectroscopically at the deep photometric minimum of the star. The Galactic motion of RZ Psc calculated with new Gaia DR2 astrometric data suggests possible membership in Cas-Tau OB association with an age of t = 20−5+3 t = 20 − 5 + 3 $ t=20^{+3}_{-5} $ Myr.
ABSTRACT
It has been shown that during the burst of accretion activity observed in UX Ori-type star RZ Psc in 2013, the accretion rate increased approximately by an order of magnitude. This means ...that the accretion process at the late stages of the pre-main sequence evolution is very unstable. Using the spectra obtained during this episode, we have studied the magnetospheric emission in the H α line. Models of magnetospheric accretion are calculated to obtain the parameters of the magnetosphere from this observation. In this work, we have taken into account the influence of the recombination delay effect during gas motion in the stellar magnetosphere. The accounting for this effect and the presence of the magnetospheric absorption in the IR Ca ii triplet lines and its absence in D Na i resonance lines allowed us to place a lower limit on the temperature in the magnetosphere at $\approx 10\, 000$ K, which significantly improved precision of our estimate of accretion rate. According to the best-fitting model, the logarithm of accretion rate is $\log \dot{M} = -10.1\pm 0.3$ ($\dot{M} \approx 7\times 10^{-11}\ \mathrm{M_\odot \, yr^{-1}}$) and the inclination angle of RZ Psc is 43° ± 3°. It is less than the inclination, typical for the UX Ori stars (about 70°), that explains the weak photometric variability of this star. Using the obtained accretion rate and magnetosphere radius, we estimate the strength of the dipole component of the magnetic field of RZ Psc ≈ 0.1 kGs.
Context.
Rotation periods inferred from the magnetic variability of some Ap stars are incredibly long, exceeding ten years in some cases. An explanation for such slow rotation is lacking.
Aims.
This ...paper attempts to provide an explanation of the super-slow rotation of the magnetic and thermal patterns of Ap stars in terms of the longitudinal drift of the unstable disturbances of the kink-type (Tayler) instability of their internal magnetic field.
Methods.
The rates of drift and growth were computed for eigenmodes of Tayler instability using stellar parameters estimated from a structure model of an A star. The computations refer to the toroidal background magnetic field of varied strength.
Results.
The non-axisymmetric unstable disturbances drift in a counter-rotational direction in the co-rotating reference frame. The drift rate increases with the strength of the background field. For a field strength exceeding the (equipartition) value of equal Alfven and rotational velocities, the drift rate approaches the proper rotation rate of a star. The eigenmodes in an inertial frame show very slow rotation in this case. Patterns of magnetic and thermal disturbances of the slowly rotating eigenmodes are also computed.
Conclusions.
The counter-rotational drift of Tayler instability eigenmodes is a possible explanation for the observed phenomenon of super-slowly rotating Ap stars.
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 Teff = 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.
RZPsc is an isolated high-latitude post-T Tauri star that demonstrates a UX Ori-type photometric activity. The star shows very weak spectroscopic signatures of accretion, but at the same time ...possesses the unusual footprints of the wind in NaiDlines. In the present work we investigate new spectroscopic observations of RZPsc obtained in 2014 during two observation runs. We found variable blueshifted absorption components (BACs) in lines of the other alcali metals, Ki 7699 A and Caii IR triplet. We also confirmed the presence of a weak emission component in the H alpha line, which allowed us to estimate the mass accretion rate on the star as M< or = 7 x 10 super(-12)M sub(middo t in circle)yr super(-1). We could not reveal any clear periodicity in the appearance of BACs in sodium lines. Nevertheless, the exact coincidence of the structure and velocities of the Nai D absorptions observed with the interval of about one year suggests that such a periodicity should exist.
Results from a study of low resolution spectra and kinematics of the star V1117 Her located at a high galactic latitude b = +33°.8 are presented. It is shown that this star has A7 IV photospheric ...class, luminosity L ≈ 26 L
ʘ
, and spectral signs of accretion activity. This confirms its previous classification as a young Ae Herbig star with photometric UX Ori type variability. In addition, the parallax of V1117 Her in the GAIA DR2 catalog corresponds to a distance of D ≈ 1.4 kpc to it, which represents a height Z ≈ 800 pc of the star above the galactic plane. Here the kinetics of the star indicates its more probable formation in situ, outside the plane of the young disk. A possible scenario for the formation of V1117 Her is discussed briefly.
We report the discovery of mid-infrared excess emission in the young object RZ Psc. The excess constitutes ~8% of its Lbol and is well fit by a single 500 K blackbody, implying a dust-free region ...within ~0.7 AU for optically thick dust. The object displays dust obscuration events (UXOR behaviour) on a time scale that suggests dusty material on orbits of ~0.5 AU. We also report a 12.4-year cyclical photometric variability that can be interpreted as caused by perturbations in the dust distribution. The system is characterized by a high inclination, marginal extinction (during bright photometric states), a single temperature for the warm dust, and an age estimate that puts the star beyond the formation stage. We propose that the dust occultation events present a dynamical view of an active asteroid belt whose collisional products sporadically obscure the central star.
The star RZ Psc is one of the most enigmatic members of the UX Ori star family. It shows all properties that are typical for these stars (the light variability, high linear polarization in deep ...minima, the blueing effect) except for one: it lacks any signatures of youth. With the lithium line 6708 Å as a rough estimate for the stellar age, we show that the “lithium” age of RZ Psc lies between the age of stars in the Pleiades (~70 Myr) and the Orion (~10 Myr) clusters. We also roughly estimated the age of RZ Psc based on the proper motion of the star using the Tycho-2 catalog. We found that the star has escaped from its assumed birthplace near to the Galactic plane about 30−40 Myr ago. We conclude that RZ Psc is a post-UXOr star, and its sporadic eclipses are caused by material from the debris disk.
A near infrared and optical photometric study of Herbig star V517 Cyg has been carried out. The infrared data were obtained in 2003–2017 at the Campo Imperatore Observatory (Italy) with the Pulkovo ...AZT-24 telescope in the Johnson
JHK
bands. The optical light curves in the Johnson
UBVR
bands were obtained at the Maidanak observatory. Additional optical photometry from different sources (ASAS, WISE, and AAVSO) was also used. It has been shown that the behavior of V517 Cyg in the near infrared is typical for UX Ori stars. A considerable contribution to the near infrared variability is made by changes in the extinction along the line of sight; however, in the
H
and
K
bands, the influence of the disk is strong: there is a significant correlation between
V
and
J
magnitudes (
r
∼ 0.84), while
H
and
K
magnitudes poorly correlate with
V
magnitude. The amplitude of variability in the
J
band is quite large (∼1.8
m
). In the deepest minimum in
V
band (
∼ 3.6
m
) the star demonstrates quasi-periodic variations with an amplitude of ∼0.8
m
and a period of ∼19
d
(plain).; and their origin is still unclear. It is possible that these oscillations are caused by the presence of a companion, a cold T Tau star, and related to its rotation period. The spectrum of V517 Cyg reveals typical for UX Ori stars the double-peaked emission line H
α
. The NaI D lines have the inverse P Cyg profiles, which is indicative of intensive gas accretion onto the star. The accretion rate determined from the equivalent width of the H
α
line is
= 3.6 × 10
–8
per year.
RZ Psc is an isolated high-latitude post-T Tauri star that demonstrates a UX Ori-type photometric activity. The star shows very weak spectroscopic signatures of accretion, but at the same time ...possesses the unusual footprints of the wind in Na i D lines. In the present work we investigate new spectroscopic observations of RZ Psc obtained in 2014 during two observation runs. We found variable blueshifted absorption components (BACs) in lines of the other alcali metals, K i 7699 Å and Ca ii IR triplet. We also confirmed the presence of a weak emission component in the Hα line, which allowed us to estimate the mass accretion rate on the star as Ṁ ≤ 7 × 10-12M⊙ yr-1. We could not reveal any clear periodicity in the appearance of BACs in sodium lines. Nevertheless, the exact coincidence of the structure and velocities of the Na i D absorptions observed with the interval of about one year suggests that such a periodicity should exist.
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