The problem of verification of the Moore finite state machine by the statistical properties of the input and output sequences is considered. It is assumed that the initial state of the automaton is unknown. To verify the automaton, the polyhedra method is used. The results of computational experiments for four classes of non-autonomous binary shift registers are presented.

A near infrared and optical photometric study of Herbig star V517 Cyg has been carried out. Infrared data were obtained in 2003–2017 at the Campo Imperatory Observatory (Italy) with the Pulkovo telescope AZT-24 in Johnson’s \(JHK\) bands. Optical light curves in Johnson \(UBVR\) bands were obtained at the Maidanak observatory. Additional optical photometry from different sources (ASSAS, WISE, and AAVSO) was also used. It was 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 due to variable extinction along the line of sight, but the disk radiation becomes strong in the \(H\) and \(K\) bands: there is a significant correlation of \(V\) and \(J\) magnitudes (\(r \sim 0.84\)), while \(H\) and \(K\) bands correlates poorly with \(V\) band. The amplitude of variability in \(J\) is quite large (\( \sim {\kern 1pt} {{1.8}^{m}}\)). The deepest minimum (\(\Delta V \sim {{3.6}^{m}}\)) in the \(V\) band demonstrates quasi-periodic variations with an amplitude of \( \sim {\kern 1pt} {{0.8}^{m}}\) and a period of \( \sim {\kern 1pt} 19\) days, the origin of which is still unclear. It is possible that these quasi-periodic variations are related to rotation period of a second companion, a cold T Tauri star. The spectrum V517 Cyg reveals typical for UX Ori stars the double-peaked emission line Hα. The NaI D doublet has inverse P Cyg profiles, indicating intense accretion of gas onto the star. The accretion rate from an equivalent width of the Hα line is \({{\dot {M}}_{{acc}}} = 3.6 \times {{10}^{{ - 8}}}\,{{M}_{ \odot }}\) per year.

The problem of verification of the Moore finite state machine by the statistical properties of the input and output sequences is considered. It is assumed that the initial state of the automaton is unknown. To verify the automaton, the polyhedra method is used. The results of computational experiments for four classes of non-autonomous binary shift registers are presented.

$Context.$ The YSO Th 28 possesses a highly collimated jet, which clearly exhibits an asymmetric brightness of its jet lobes at optical and NIR wavelengths. There may be asymmetry in the jet plasma parameters in opposite jet lobes (e.g. electron density, temperature, and outflow velocity). $Aims.$ We examined the Th 28 jet in a 3"x3" where the jet material is collimated and accelerated. Our goal is to map the morphology and determine its physical parameters to determine the physical origin of such asymmetries. $Methods.$ We present $JHK$-spectra of Th 28 obtained with the SINFONI on the (VLT, ESO) in June-July 2015. $Results.$ The [Fe II] emission originates in collimated jet lobes. Two new axial knots are detected at 1" in the blue lobe and 1".2 in the red lobe. The H$_2$ radiation is emitted from an extended region with a radius of $\gtrsim270$ au, which is perpendicular to the jet. The PV diagrams of the bright H$_2$ lines reveal faint H$_2$ emission along both jet lobes as well. The compact and faint H I emission (Pa$\beta$ and Br$\gamma$) comes from two regions, namely from a spherical region around the star and from the jet lobes. The size of the jet launching region is derived as 0".015 ($\sim$3 au at 185 pc), and the initial opening angle of the Th 28 jet is $\sim28^0$, which makes this jet substantially less collimated than most jets from other CTTs. $Conclusions.$ The emission in [Fe II], H$_2$, and H I lines suggests a morphology in which the ionised gas in the disc appears to be disrupted by the jet. The resolved disc-like H$_2$ emission most likely arises in the disc atmosphere from shocks caused by a radial uncollimated wind. The asymmetry of the [Fe II] photocentre shifts with respect to the jet source arises in the immediate vicinity of the driving source of Th28 and suggests that the observed brightness asymmetry is intrinsic as well.

R Aqr is a symbiotic binary system consisting of a Mira variable with a pulsation period of 387 days and a hot companion which is presumably a white dwarf with an accretion disk. This binary system is the source of a prominent bipolar gaseous outflow. We use high spatial resolution and sensitive images from the Hubble Space Telescope to identify and investigate the different structural components that form the complex morphology of the R Aqr jet . Methods. We present new high-resolution HST WFC3/UVIS narrow-band images of the R Aqr jet obtained in 2013/14 in the light of the [OIII] 5007, [OI] 6300, [NII] 6583, and Ha emission lines. These images also allow us to produce detailed maps of the jet flow in several line ratios such as [OIII]/[OI] and [NII]/[OI] which are sensitive to the outflow temperature and its hydrogen ionisation fraction. The new emission maps together with archival HST data are used to derive and analyse the proper motion of prominent emitting features which can be traced over 20 years with the HST observations. The images reveal the fine gas structure of the jet out to distances of a few ten arcseconds from the central region, as well as in the innermost region, within a few arcseconds around the stellar source. They reveal for the first time the straight highly-collimated jet component which can be traced to up to 900 AU in the NE direction. Images in [OIII], [OI], and [NII] clearly show a helical pattern in the jet beams which may derive from the small-scale precession of the jet. The highly-collimated jet is accompanied by a wide opening angle outflow which is filled by low excitation gas. The position angles of the jet structures as well as their opening angles are calculated. Our measurements of the proper motions of some prominent emission knots confirm the scenario of gas acceleration during the propagation of the outflow.

Context. Unlike young open clusters (with ages < 250 Myr), the Hyades cluster (age ~ 600 Myr) has a clear deficit of very low-mass stars (VLM) and brown dwarfs (BD). Since this open cluster has a low stellar density and covers several tens of square degrees on the sky, extended surveys are required to improve the statistics of the VLM/BD objects in the cluster. Aim. We search for new VLM stars and BD candidates in the Hyades cluster to improve the present-day cluster mass function down to substellar masses. Methods. An imaging survey of the Hyades with a completeness limit of 21. m 5 in the R band and 20. m 5 in the I band was carried out with the 2k × 2k CCD Schmidt camera at the 2 m Alfred Jensch Telescope in Tautenburg. We performed a photometric selection of the cluster member candidates by combining results of our survey with 2MASS JHK s photometry Results. We present a photometric and proper motion survey covering 23.4 deg 2 in the Hyades cluster core region. Using optical/IR colour-magnitude diagrams, we identify 66 photometric cluster member candidates in the magnitude range 14. m 7 < I < 20. m 5. The proper motion measurements are based on several all-sky surveys with an epoch difference of 60–70 yr for the bright objects. The proper motions allowed us to discriminate the cluster members from field objects and resulted in 14 proper motion members of the Hyades. We rediscover Hy 6 as a proper motion member and classify it as a substellar object candidate (BD) based on the comparison of the observed colour-magnitude diagram with theoretical model isochrones. Conclusions. With our results, the mass function of the Hyades continues to be shallow below ~0.15 M ⊙ indicating that the Hyades have probably lost their lowest mass members by means of dynamical evolution. We conclude that the Hyades core represents the “VLM/BD desert” and that most of the substeller objects may have already left the volume of the cluster.

Context. Little is known about the population of the Coma Berenices open cluster (age similar to 500 Myr) below 0.2 M-circle dot, and statistics show that there is a prominent deficit of very low-mass objects in this mass range compared to younger open clusters with ages of <250 Myr.Aims. We search for very low-mass stars and substellar objects (brown dwarfs) in the Coma open cluster to derive the present-day cluster mass function below 0.2 M-circle dot.Methods. An imaging survey of the Coma open cluster in the R- and I-bands was carried out with the 2k x 2k CCD Schmidt camera at the 2-m telescope in Tautenburg. We performed a photometric selection of the cluster member candidates by combining results of our survey with 2MASS JHK(s) photometry. We also analysed low-resolution optical spectroscopic observations of a sample of 14 of our stellar cluster member candidates to estimate their spectral types and luminosity.Results. We present a photometric survey covering 22.5 deg(2) around the Coma open cluster centre with a completeness limit of 21.(m)5 in the R-band and 20.(m)5 in the I-band. Using optical/IR colour-magnitude diagrams, we identify 82 very low-mass cluster member candidates in the magnitude range 14.(m)7 < I < 20.(m)1. Five of them have luminosities and colour indices consistent with brown dwarfs. We calculate a mass spectrum of the very low-mass end of the cluster under the assumption that all selected candidates are probable cluster members. The calculated present-day mass function (dN/dm approximate to m(-alpha)) can be divided into two parts with a slope of alpha = 0.6 in the mass interval 0.2 > M-star > 0.14 M-circle dot and alpha similar to 0 in 0.14 > M-star > 0.06 M-circle dot.Conclusions. Our analysis of the spectroscopy of 14 objects shows that they are very low-mass MV-dwarfs of spectral type and luminosity consistent with Coma open cluster membership. This suggests that the membership probability of our other candidates may be high. Our results suggest that the mass function of the Coma open cluster can be traced towards substellar objects, but comparison with a mass spectra of younger clusters indicates that the Coma open cluster has probably lost its lowest mass members by means of dynamical evolution.

Context. Jets from young stars can be highly asymmetric and have multiple velocity components.Aims. To clarify the origin of jet asymmetries and constrain the launch mechanism, we study as a test case the physical and kinematical structure of the prototypical asymmetric flow emitted by DG Tau B.Methods. The analysis of deep, high spectral resolution observations taken with the KECK telescope allows us to infer the properties and the spatial distribution of the velocity components in the two jet lobes. From selected line ratios we derive the gas physical conditions (the electron and total density, n(e) and n(H), the ionisation fraction, x(e), and the temperature, T-e), as a function of the distance from the source and the gas velocity. The presence of dust grains in the jet is investigated by estimating the gas-phase abundance of calcium with respect to its solar value.Results. The detected lines show broad velocity profiles at the base of the jet (up to similar to 100 km s(-1)), where up to three velocity components are detected. At 5 '' from the source, however, only the denser and more excited high-velocity components survive and the lines are narrower (similar to 10-30 km s(-1)). The jet is strongly asymmetric in the velocity and in its physical structure. The red lobe, which is slower (similar to 140 km s(-1)) and more collimated (opening angle: alpha similar to 34 degrees), presents low ionisation fractions (x(e) similar to 0.10.4) and temperatures (T-e < 5 x 10(3) K), while the total density is up to similar to 2.5 x 10(4) cm(-3). The blue lobe, faster (similar to 320 km s(-1)) and less collimated (alpha similar to 14 degrees), is also less dense (nH < 10(4) cm(3)), but highly excited (Te up to similar to 5 x 10(4) K and xe up to 0.9). The estimated massloss rate turns out to be similar in the two lobes (similar to 68 x 10(9) M-circle dot yr(-1)), while the flux of the linear momentum is three times higher in the blue one (similar to 2.5 x 10(-7) M-circle dot yr(-1) km s(-1)). Calcium is strongly depleted with respect to its solar abundance, indicating that the jet contains dust grains. The depletion is lower for higher velocities, which is consistent with dust destruction by shocks.Conclusions. The similar massloss rate in the two lobes suggests that the ejection power is comparable on the two sides of the system, as expected from a magnetocentrifugal ejection mechanism, and that the observed asymmetries are caused by a different mass load and propagation properties in an inhomogeneous environment. The presence of dust grains implies that the jet is generated from a region of the disc extending beyond the dust sublimation radius.

A well-collimated bipolar jet emanating from the classic T Tauri star RW Aur A (HH 229) has been traced out to 15″ in the redshifted [2] and over 100″ in the blueshifted lobe [3]. Long-slit spectra of the RW Aur jet were taken on 10. Dec. 2000 with the STIS spectrograph on board the HST. The spectrographslit of width 0″:1 and length 10″ was moved across the jet in seven positions from NW to SE, keeping it parallel to the jet axis. As a result, seven spectra covering the jet in both dimensions were obtained. The observations taken with the G750M grating cover the three prominent forbidden emission doublets – [O I] (λλ 6300,6363, [N II] λλ 6548,6583, and [S II] λλ 6716,6731. The current study presents a continuation of the analysis of the HST/STIS spectroscopy of the RW Aur jet started in Woitas et al. [5]. For extraction of the physical quantities we followed the well-established method described in Bacciotti and Eislöffel [1].

We present the results of new spectral diagnostic investigations applied to high-resolution long-slit spectra of the RW Aur bipolar jet obtained with HST/STIS. The spectra include the forbidden doublets [O I] 6300,6363 \AA, [S II] 6716,6731 \AA, and [N II] 6548, 6583 \AA that we utilized to determine electron density, electron temperature, hydrogen ionisation fraction, total hydrogen density, radial velocity and the mass outflow rate. We were able to extract the parameters as far as 3".9 in the red- and 2".1 in the blueshifted beam. The RW Aur jet appears to be the second densest outflow from a T Tauri star studied so far, but its other properties are quite similar to those found in other jets from young stars. The overall trend of the physical parameters along the first few arcseconds of the RW Aur jet is similar to that of HH 30 and DG Tau and this can reflect analogies in the mechanisms operating in that region, suggesting the same engine is accelerating the jets in the T Tauri stars with outflows. Our study of the RW Aur jet indicates for the first time that, despite the detected marked asymmetries in physical and kinematic properties between the two lobes, the mass outflow rates in the two lobes are similar. This appears to indicate that the central engine has constraining symmetries on both sides of the system, and that the observed asymmetries are probably due to different environmental conditions.

Context. LkH alpha 233 is a Herbig Ae/Be star with a collimated bipolar jet. As such, it may be a high-mass analogue to the classical T Tauri stars and their outflows.Aims. We investigate optical forbidden lines along the LkH alpha 233 jet to determine physical parameters of this jet (electron density ne, hydrogen ionisation fraction x(e), electron temperature T(e)). The knowledge of these parameters allows us a direct comparison of a jet from a Herbig star with those from T Tauri stars.Methods. We present the results of HST/STIS and WFPC2 observations of LkH alpha 233 and its environment. These are the first observations of this object with a spatial resolution of <= 0 ''.1 at optical wavelengths. Our STIS data provide spectroscopic maps that allow us to reconstruct high angular resolution images of the bipolar jet from LkH alpha 233 covering the first approximate to 2000 AU from the star in the blueshifted outflow lobe and approximate to 4000 AU in the redshifted lobe. These maps are analysed with a diagnostic code that yields n(e), x(e), T(e), and mass density n(H) within the jet.Results. The WFPC2 images in broad-band filters clearly show a dark lane caused either by a circumstellar disk or a dust torus. The circumstellar environment of LkH alpha 233 can be interpreted as a conical cavity that was cleared by a bipolar jet. In this interpretation, the maximum of the optical and near-infrared brightness distribution does not coincide with the star itself which is, in fact, deeply extincted. In the blueshifted lobe, ne is close to or above the critical density for [SII] lines (2.5 x 10(4) cm(-3)) in the first arcsecond and decreases with distance from the source. The ionisation x(e) approximate to 0.2-0.6 gently rises for the first 500 AU of the flow and shows two re-ionisation events further away from the origin. The electron temperature T(e) varies along the flow between 104 K and 3 x 104 K. The n(H) is between 3 x 10(3) and 10(5) cm(-3), and the mass flux. M approximate to 10(-8)- 10(-7) M(circle dot) yr(-1). The (radial) outflow velocities are approximate to 80-160 km s(-1), and they appear to increase with distance from the source. In the redshifted lobe, the excitation conditions are quite different: T(e), n(e), x(e), and n(H) are all lower than in the blueshifted lobe, but have the same order of magnitude.Conclusions. All these derived parameters are just beyond or at the upper limits of those observed for classical T Tauri star jets. This may indicate that the flows from the higher mass Herbig stars are indeed scaled-up examples of the same phenomenon as in T Tauri stars.

Context. T Tauri stars exhibit variability on all timescales, whose origin is still debated. On WTTS the variability is fairly simple and attributed to long-lived, ubiquitous cool spots.Aims. We investigate the long term variability of WTTS, extending up to 20 years in some cases, characterize it statistically and discuss its implications for our understanding of these stars.Methods. We have obtained a unique, homogeneous database of photometric measurements for WTTS extending up to 20 years. It contains more than 9000 UBVR observations of 48 WTTS. All the data were collected at Mount Maidanak Observatory (Uzbekistan) and they constitute the longest homogeneous record of accurate WTTS photometry ever assembled.Results. Definitive rotation periods for 35 of the 48 stars are obtained. Phased light curves over 5 to 20 seasons are now available for analysis. Light curve shapes, amplitudes and colour variations are obtained for this sample and various behaviors exhibited, discussed and interpreted.Conclusions. Our main conclusion is that most WTTS have very stable long term variability with relatively small changes of amplitude or mean light level. The long term variability seen reflects modulation in the cold spot distributions. Photometric periods are stable over many years, and the phase of minimum light can be stable as well for several years. On the long term, spot properties do change in subtle ways, leading to secular variations in the shape and amplitudes of the light curves.