Hvar Observatory Research Articles

Validation of the CME Geomagnetic Forecast Alerts Under the COMESEP Alert System

Under the European Union 7th Framework Programme (EU FP7) project Coronal Mass Ejections and Solar Energetic Particles (COMESEP, http://comesep.aeronomy.be), an automated space weather alert system has been developed to forecast solar energetic particles (SEP) and coronal mass ejection (CME) risk levels at Earth. The COMESEP alert system uses the automated detection tool called Computer Aided CME Tracking (CACTus) to detect potentially threatening CMEs, a drag-based model (DBM) to predict their arrival, and a CME geoeffectiveness tool (CGFT) to predict their geomagnetic impact. Whenever CACTus detects a halo or partial halo CME and issues an alert, the DBM calculates its arrival time at Earth and the CGFT calculates its geomagnetic risk level. The geomagnetic risk level is calculated based on an estimation of the CME arrival probability and its likely geoeffectiveness, as well as an estimate of the geomagnetic storm duration. We present the evaluation of the CME risk level forecast with the COMESEP alert system based on a study of geoeffective CMEs observed during 2014. The validation of the forecast tool is made by comparing the forecasts with observations. In addition, we test the success rate of the automatic forecasts (without human intervention) against the forecasts with human intervention using advanced versions of the DBM and CGFT (independent tools available at the Hvar Observatory website, http://oh.geof.unizg.hr). The results indicate that the success rate of the forecast in its current form is unacceptably low for a realistic operation system. Human intervention improves the forecast, but the false-alarm rate remains unacceptably high. We discuss these results and their implications for possible improvement of the COMESEP alert system.

The Hvar survey for roAp stars

The 60 known rapidly oscillating Ap (roAp) stars are excellent laboratories to test pulsation models in the presence of stellar magnetic fields. Our survey is dedicated to search for new group members in the Northern Hemisphere. We attempt to increase the number of known chemically peculiar stars that are known to be pulsationally unstable. About 40 h of new CCD photometric data of 21 roAp candidates, observed at the 1m Austrian-Croatian Telescope (Hvar Observatory) are presented. We carefully analysed these to search for pulsations in the frequency range of up to 10mHz. No new roAp star was detected among the observed targets. The distribution of the upper limits for roAp-like variations is similar to that of previoius similar efforts using photomultipliers and comparable telescope sizes. In addition to photometric observations, we need to consolidate spectroscopic information to select suitable targets.

The Hvar survey for roAp stars

Context. The rapidly oscillating Ap (roAp) stars exhibit short time scale photometric and/or radial velocity variations, which are most important to test current pulsation models as well as our assumptions of the atmospheric structure characteristics. In addition, their chemical peculiarity makes them very interesting for probing stellar formation and evolution in the presence of a global magnetic field. To date, only a limited number of about 45 roAp stars are known.Aims. In order to increase the sample, we obtained photometric time series of 20 good roAp candidates to search for pulsations. Methods. We present the time series analysis of about 60 h of CCD photometry taken at the 1 m Austrian-Croatian Telescope (Hvar Observatory) and derive effective temperatures for the programme objects.Results. The upper amplitude limits of the Fourier spectra are typically below 2 mmag in Bessell B with one good candidate for follow-up observations to find possible pulsation. In addition, we present a list of further roAp candidates, worth to be (re)investigated.

Applying the Steepest Descent Method with BINSYN on RY Per Photometry

AbstractRecent studies of the Algol-type binary RY Per presented strong evidence that there is an accretion disk around the primary in the system. We used new UBV photometry from Hvar Observatory and the BINSYN software package in order to determine the basic parameters of the disk. The search for the best parameter set was performed with a fully automated steepest descent method. The resulting disk is large and visible at all orbital phases. Somewhat surprising is the large mass transfer rate which should be tied with, currently unreported, secular period changes.

Properties and nature of Be stars

' Department of Physics and Astronomy, Michigan State University, E. Lansing, MI, 48824 and Affiliate Professor, Department of Astronomy, University of Washington, Seattle, WA 98195, USA e-mail: linnell@astro.washington.edu 2 Astronomical Institute of the Charles University, Faculty of Mathematics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic 3 Astronomical Institute, Academy of Sciences, 251 65 Ondrejov, Czech Republic e-mail: hec@sunstel. asu. cas. cz 4 Hvar Observatory, Faculty of Geodesy, Kaciceva 26, 10000 Zagreb, Croatia e-mail: hbozic (dsudar, rdomagoj)@hvar.geof. hr 5 Department of Physics and Astronomy, University of Victoria, PO Box 3055 STN CSC, Victoria, B.C., V8W 3P6, Canada e-mail: yang@uvastro.plays..uvic.ca 6 Dept. of Astronomy, University of Guanajuato, 36000 Guanajuato, GTO, Mexico Aims. We include existing photometric and spectroscopic material with new observations in a detailed study of the Be+F binary V360 Lac. Methods. We used the programs FOTEL and KOREL to derive an improved linear ephemeris and to disentangle the line profiles of both binary components and telluric lines. The BINSYN software suite (described in the paper) is used to calculate synthetic light curves and spectra to fit the UBV photometry, an IUE spectrum, blue and red ground-based spectra, and observed radial-velocity curves. Results. The observations provide evidence of circumstellar matter in the system. The system model shows that the Be primary star is critically rotating, and that the synchronously rotating secondary star fills its Roche lobe. The primary star has a mass of 7.45 M ⊙ . Radial-velocity observations establish a mass ratio of 0.163. Light curve synthesis demonstrates that the observed light curves are controlled largely by tidal distortion and irradiation of the massive primary by the less massive secondary. Synthetic spectra fit both blue and red observed spectra with the exception of spectral lines affected by circumstellar matter in the system. The synthetic spectra allow for gravity darkening and are consistent with critical rotation of the primary. Synthetic spectrum fits to a dereddened IUE spectrum produce a calculated system distance of 512 pc. This distance is 2σ beyond the Hipparcos distance.

Rapid Light Variations of the Bright Be Star ϕ Per

AbstractAn analysis of the UBV photometric measurements obtained at Hvar Observatory and Hp HIPPARCOS photometry has been performed in order to disclose the suspected rapid periodic variations of the Be star ϕ Per. The reliability of the derived 0.5 day period is examined and the difficulties of detecting the period due to the complex character of the light variations on the longer time-scales are outlined. Possible explanations of these rapid variations are briefly discussed.

UBV photometry of Be stars at Hvar: 1972–1990

A summary of results of the systematic UBV photoelectric monitoring of bright northern Be stars carried out at the Hvar Observatory betwen 1972 and 1990 is presented. Altogether, 76 Be stars of all luminosity classes were observed and 13848 UBV measurements secured. Simultaneously, 9648 UBV measurements of 48 check stars (most of them of early spectral types) were obtained. A careful transformation of all observations into the standard Johnson system allowed detection and monitoring of even very mild long-term light and colour variations of these objects. Almost all early-type Be stars in the sample turned out to be variable. For several stars phase-locked light variations related to their binary nature were establihsed. Sudden brightenings, on a time scale of a days, were detected for o Cas and QR Vul.

Photometric characteristics of the Be stars: almost twenty years of UBV monitoring at the Hvar observatory

Since their discovery (by Father Secchi in 1866) until the end of sixties, Be stars were not a subject of any systematic studies of their possible light and colour variations. Already at that time, the astronomical literature contained ample evidence showing that a number of Be stars were light variables. However, almost all such findings resulted as by-products of studies of different or wider groups of objects. Feinstein (1968) was probably the first who pointed out explicitly that many Be stars are light variables. A pioneering study which was aimed at the detection of light variations of a large group of Be stars by means of differential photoelectric photometry was carried out by Haupt & Schroll (1974).

KX Andromedae: Possibly a Strongly Interacting Binary

Although KX And (HD 218393, MWC 397) has been observed since the beginning of our century, we have no reliable model of this peculiar emission-line object. Published papers (e.g. Plavec et al. 1982; Kriz and Harmanec 1975 and references therein) indicate that it is a B+K W Ser-type binary with a period of 38.9 days. This paper presents a summary of intensive observations carried out during the last fifteen years.The observational material used consists of 65 coude spectra obtained with the Ondrejov 2-m telescope, UBV photometry obtained at Hvar Observatory and 28 archival IUE images. The radial-velocity and photometric data are combined with those found in the literature. A PDM period search over the interval 1 to 1000 days unambiguously indicates the 38.9-day period both in RV and photometric data.

On the correlation of microwave bursts with the H α flares

High correlation between microwave bursts and H α flares has already been reported. However, Solar Maximum Year cooperation made it possible to do simultaneous observations of selected active regions with good spatial resolution. In this paper the results of the direct comparison of solar microwave recordings at the Metsähovi Radio Research Station and H α films at the Hvar Observatory are reported. This comparison reveals that the correlation of microwave gradual rise and fall (GRF) events (time scale tens of minutes) with H α flares is practically 100 percent. On the other hand the correlation of the impulsive microwave bursts (time scale tens of seconds) with H α flares is low. From this it can be concluded that the main contribution to the microwave GRF bursts comes from thermal radiation.

Structure of the Gaseous Disk in RX Cas

RX Cas appers to be a long-period Algol-like binary with very fast mass exchange (Struve 1944). In the period 1975-1977, this star was observed photometrically by Arsenijevič, Grygar, Harmanec, Horn, Koubský, Kříž and Pavlovski at Hvar Observatory (Yugoslavia) and by Zverko at Skalnaté Pleso Observatory (Czechoslovakia). The resulting UBV light curves seem to be rather peculiar, for the following reasons:1) Combining our observations with the older ones, we obtain the following formula for the times of minima: The period increase is surprisingly high.2) The scatter of observed points is considerable (about 0.2 mag.) and cannot be caused by observational errors. It corresponds to short period light variations on the time scale of several days.3) After J.D. 24422660, the brightness of the whole system decreased in all colours. This decrease is about 0.2 mag. in V colour and 0.5 mag. in U colour. Only after J.D. 2442900 the brightness increased again. Such a behaviour confirms the reality of old observations by Gaposchkin (1944) and Martynov (1950) who found a long-term light variation with a period of approximately 500 days.4) The part of the light curve around the phase 0.75 is definitely much lower than the corresponding part around the phase 0.25. This effect is most pronounced in the ultraviolet; the depression around the phase 0.75 is much deeper than the secondary minimum. This behaviour is opposite to the behaviour of dwarf novae. Instead of a bright shoulder connected with a bright spot, we observe some darkening.

Two-color search for the posteclipse brightening of Io

Blue-violet photoelectric photometry of a reappearance of Io on 10 October 1974 is presented. Observations were made with a single-beam photometer on the Hvar Observatory 65-cm telescope. A brightness anomaly of about 0.15 and 0.25 mag in V and B, respectively, was detected, but owing to the relativity large estimated errors, 0.04 and 0.05 mag, respectively, detection is regarded astentative. The wavelength dependence, reported previously by some investigators, was confirmed. The urgent need of multicolor photometry is briefly stressed.