Wise Observatory Research Articles

Multi-wavelength photometric study of five contact binaries in the field of globular cluster M4

Binary stars are believed to be key determinants in understanding globular cluster evolution. In this paper, we present the Multi-band photometric analyses of five variables in the nearest galactic globular cluster M4, from the observations of CASE, M4 Core Project with HST for four variables (V48, V49, V51, and V55) and the data collected from T40 and C18 Telescopes of Wise Observatory for one variable (NV4). The light curves of five binaries are analysed using the Wilson–Devinney method (WD) and their fundamental parameters have been derived. A period variation study was carried out using times of minima obtained from the literature for four binaries and the nature of the variation observed is discussed. The evolutionary state of systems is evaluated using M-R diagram, correlating with that of a few well-studied close binaries in other globular clusters. Based on the data obtained from the Gaia DR3 database, a three-dimensional Vector-Point Diagrams (VPD) was built to evaluate the cluster membership of the variables, and two out of them (V49 and NV4) were found to be not cluster members.

Changing material around (2060) Chiron revealed by an occultation on December 15, 2022

We were able to accurately predict the shadow path and successfully observe an occultation of a bright star by Chiron on December 15, 2022. The Kottamia Astronomical Observatory in Egypt did not detect the occultation by the solid body, but we found three extinction features in the light curve that had symmetrical counterparts with respect to the central time of the occultation. One of the features is broad and shallow, whereas the other two features are sharper, with a maximum extinction of ∼25% at the achieved spatial resolution of 19 km per data point. From the Wise Observatory in Israel, we detected the occultation caused by the main body and several extinction features surrounding the body. When all the secondary features are plotted in the sky plane, we find that they can be caused by a broad ∼580 km disk with concentrations at radii of 325 ± 16 km and 423 ± 11 km surrounding Chiron. At least one of these structures appears to be outside the Roche limit. The ecliptic coordinates of the pole of the disk are λ = 151° ±8° and β = 18° ±11°, in agreement with previous results. We also reveal our long-term photometry results, indicating that Chiron had suffered a brightness outburst of at least 0.6 mag between March and September 2021 and that Chiron was still somewhat brighter at the occultation date than at its nominal pre-outburst phase. The outermost extinction features might be consistent with a bound or temporarily bound structure associated with the brightness increase. However, the nature of the brightness outburst is unclear, and it is also unclear whether the dust or ice released in the outburst could be feeding a putative ring structure or whether it is emanating from it.

Continuum reverberation mapping of MCG 08-11-011

Aims. We report the results from a photometric reverberation mapping campaign carried out with the C18 telescope at the Wise Observatory from 2019 to 2020, targeting the active galactic nucleus (AGN) MCG 08-11-011. The monitoring was conducted on a daily basis with specially designed narrow-band filters, spanning from optical to near-infrared wavelengths (∼4000 to 8000 Å) and avoiding prominent broad emission lines. We aim to measure inter-band continuum time lags, determine the size–wavelength relation, and estimate the host-subtracted AGN luminosity for this system. Methods. We used the point-spread function photometry to extract the continuum light curves and measure the inter-band time lags using several methods, including the interpolated cross-correlation function, the z-transformed discrete correlation function, a von Neumann estimator, JAVELIN (in spectroscopic and photometric mode), MICA, and a multivariate correlation function. Results. We find wavelength-dependent lags, τ(λ), up to ∼7 days between the multiband light curves of MCG 08-11-011. The observed lags are larger than predictions based on standard thin-disk theory by a factor of ∼3 − 7. We discern a significantly steeper (τ ∝ λ4.74) size-wavelength relation than the τ ∝ λ4/3 expected for a geometrically thin and optically thick accretion disk, which may result from the contribution of diffuse continuum emission to the flux. These results are similar to those found by previous continuum reverberation mapping campaigns.

The Effects of Fog on the Atmospheric Electrical Field Close to the Surface

Ground-based measurements of the atmospheric electric field have been recorded continuously since 2013 at the Wise Observatory, located in the Negev Desert Highland in southern Israel. The data have been used for defining the characteristics of fair weather and to identify the signatures of dust storms, lightning activity, and clouds. We report here on new results from observations of the variability of the electric field (transformed into the potential gradient, PG) during several foggy days, along with meteorological data on wind speed and relative humidity. The results show a substantial increase in the electric field (up to 400–650 V m−1) compared with the mean fair weather values observed at the site (180–190 V m−1). This increase is especially clear during times of high relative humidity values (95%+) and low wind speed (<3 m s−1). This increase is likely a consequence of the reduction in the atmospheric conductivity at low levels, due to the attachment of charge carriers to fog droplets. Based on this discovery, it is suggested that continuously monitoring the electric field may offer an additional operational tool to alert for the onset and termination of fog at specific locations, such as airports and harbors, where this nowcasting capability is required.

Galaxy And Mass Assembly (GAMA): Data Release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

ABSTRACT In Galaxy And Mass Assembly Data Release 4 (GAMA DR4), we make available our full spectroscopic redshift sample. This includes 248 682 galaxy spectra, and, in combination with earlier surveys, results in 330 542 redshifts across five sky regions covering ∼250 deg2. The redshift density, is the highest available over such a sustained area, has exceptionally high completeness (95 per cent to rKiDS = 19.65 mag), and is well-suited for the study of galaxy mergers, galaxy groups, and the low redshift (z < 0.25) galaxy population. DR4 includes 32 value-added tables or Data Management Units (DMUs) that provide a number of measured and derived data products including GALEX, ESO KiDS, ESO VIKING, WISE, and HerschelSpace Observatory imaging. Within this release, we provide visual morphologies for 15 330 galaxies to z < 0.08, photometric redshift estimates for all 18 million objects to rKiDS ∼ 25 mag, and stellar velocity dispersions for 111 830 galaxies. We conclude by deriving the total galaxy stellar mass function (GSMF) and its sub-division by morphological class (elliptical, compact-bulge and disc, diffuse-bulge and disc, and disc only). This extends our previous measurement of the total GSMF down to 106.75 M$_{\odot } \, h_{70}^{-2}$ and we find a total stellar mass density of ρ* = (2.97 ± 0.04) × 108 M$_{\odot } \, h_{70}$ Mpc−3 or $\Omega _*=(2.17 \pm 0.03) \times 10^{-3} \, h_{70}^{-1}$. We conclude that at z < 0.1, the Universe has converted 4.9 ± 0.1 per cent of the baryonic mass implied by big bang Nucleosynthesis into stars that are gravitationally bound within the galaxy population.

The Great Slump: Mrk 926 reveals discrete and varying Balmer line satellite components during a drastic phase of decline

Aims.Mrk 926 is known to be a highly variable active galactic nucleus. Furthermore, it is known to show very broad line profiles. We intended to study the continuum and line profile variations of this object with high temporal resolution in order to determine its broad-line region structure and to derive its black hole mass.Methods.We carried out a high-cadence spectroscopic variability campaign of Mrk 926 with the 10m HET telescope, aided by photometricV-band data taken with the C18 telescope at the Wise Observatory, over a period of about five months. We extracted spectroscopic continuum and line light curves, and computed cross-correlation functions (CCFs) as well as velocity-resolved CCFs with respect to the combined spectroscopic and photometricV-band light curve.Results.The continuum luminosity of Mrk 926 showed a drastic decrease during our campaign. The luminosity dropped to less than 50% of its original luminosity within only 2.5 months. Furthermore, the spectra of Mrk 926 show complex and very broad Balmer line profiles, including outer Balmer satellites ranging from ±5000 to ±13 000 km s−1. The integrated Hα, Hβ, and He Iλ5876 line light curves are delayed relative to the continuum light curve. The Hαand Hβlines show two velocity-delay structures in the central part of their line profile (within ±5000 km s−1), at ∼10 and ∼57 light-days and at ∼5 and ∼48 light-days, respectively. These structures might be interpreted as the upper and lower halves of an ellipse in the velocity-delay plane, which might be the signature of a line-emitting ring, inclined by ∼50° to the line of sight and orbiting the black hole at radii,R, of 33.5 and 26.5 light-days. We determined continuum luminosities, log(λ Lλ/erg s−1), of 43.68–44.13, which are in good agreement with the establishedRBLR − LAGNrelation. Adopting delays of 33.5 and 26.5 days for Hαand Hβ, respectively, we derive a black hole mass of (1.1 ± 0.2)×108 M⊙; this indicates a low Eddington ratio, which decreased from 8 to 3 percent during our campaign. The Balmer satellite components show a higher correlation coefficient with respect to the continuum than the central line profile, and their response to the continuum variations is on the order of only 3 − 5 days. We attribute this to the central line segment and the Balmer satellites having different, spatially distinct regions of origin.

The Response of Surface-Level Atmospheric Electrical Parameters in Israel to Severe Space Weather Events

We report on ground-based measurements of the atmospheric electric field (Ez) and current density (Jz) that were conducted from Israel at two locations. At the Mt. Hermon station (34.45 N, 2020 m AMSL) located in northern Israel near the Syrian-Lebanon border and at the Wise astronomical observatory in the Negev desert highland plateau of southern Israel (31.18 N, 870 m AMSL). We investigated possible effects of strong, short-term solar events that occurred during days that are defined meteorologically as fair-weather days. The first case study (St. Patrick Day, 17 March 2015) was classified as the strongest event of 2015. The second case study (8 Sep 2017) was categorized as the strongest event of 2017 and the 12 th strongest event on record to date. The results show that electrical parameters measured at ground level at both stations are affected during the two massive proton events and the ensuing geomagnetic storms. We deduce that our stations are both near the detection threshold of global electrical circuit response to solar disturbances because the magnetospheric shielding is strong enough to stop most of the flux of energetic particles, almost obscuring noticeable impacts that are above the daily variations induced by local meteorological conditions.

ROME (Radio Observations of Magnetized Exoplanets). II. HD 189733 Does Not Accrete Significant Material from Its Exoplanet Like a T Tauri Star from a Disk

Abstract It has been asserted that the primary star in the HD 189733 system steadily accretes evaporated exospheric gases from its “hot Jupiter” companion, rather like a T Tauri star accreting from a disk. We conduct statistical and periodogram analyses of the photometric time series of the primary, as acquired by the automated photoelectric telescope, Microvariability and Oscillations of Stars, and Wise Observatory, to investigate this claim with the goal of revealing the presence of accretion shocks or photospheric accretion hotspots as are found in T Tauri systems such as AA Tau. None of the anticipated features were found. We re-analyze existing radio, optical, ultraviolet, and X-ray data within the framework of accreting T Tauri systems to determine physical quantities such as plasma density and temperature, accretion rate, and flare lengths. We find that with an accretion rate of –1011 g s−1, the star is more similar to a system that intermittently absorbs gas from sungrazing comets in outburst than classical T Tauri systems, which have accretion rates at least two orders of magnitude larger. If such accretion exists, it would result in undetectably low activity at all wavelengths. Alternatively, all of the emission properties observed thus far are in agreement with stellar activity from a magnetically active star.

Surface slopes of asteroid pairs as indicators of mechanical properties and cohesion

Asteroid pairs are those found to share similar heliocentric orbits but not positions. The leading theory suggests that each had a single progenitor that split due to rotational-fission of a weak, rubble-pile structured body. By constructing shape models of asteroid pairs from multiple-apparition observations and using a lightcurve inversion technique, we mapped the gravitational and rotational accelerations on the surfaces of these asteroids. This allows us to construct a map of local slopes on the asteroids' surfaces. In order to test for frictional failure, we determine the maximum rotation rate at which an area larger than half the surface area of the secondary member (assumed to be the ejected component) has a slope value >40 degrees, the angle of friction of lunar regolith, where loose material will begin sliding. We use this criterion to constrain the failure stress operating on the body, just before disruption at the commonly observed spin barrier of 2.2 h. Our current sample includes shape models of eleven primary members of asteroid pairs, observed from the Wise Observatory in the last decade. In the studied parameter space we find that the shape models only reach the spin barrier when their bulk density is larger than the ~2 g cm−3 measured for the rubble pile structured 25143 Itokawa, and better matches 433 Eros' value of 2.7 g cm−3, suggesting that km-sized asteroid pairs are dense compared to sub-km bodies. Assuming ejection of secondary components that are larger than those observed (up to the maximal size allowing separation), can also increase the spin barrier of the asteroids, thus supporting the previously suggested scenario of continuous disruption of the secondary. In addition, cohesion levels of hundreds of Pascals are also required to prevent these shape models from disrupting at spin rates slower than the usual spin barrier.

Electrical properties of the 8–12th September, 2015 massive dust outbreak over the Levant

We report new electrical measurements conducted during the massive dust outbreak that occurred over the Levant in September 08–12, 2015. That event was one of the strongest dust storms on record and engulfed the entire region for 5 consecutive days, over Iraq through Syria, Jordan, Israel, Lebanon, Cyprus and Egypt. At its peak, Aerosol Optical Thickness of 4.0 was measured in southern Israel. Ground-based measurements of the electrical field (Ez) and current density (J) were conducted at the Wise Observatory (WO) in Mizpe-Ramon (30°35′N, 34°45′E) and near the top of Mt. Hermon (30°24′N, 35°51′E). During the dust outbreak very large fluctuations in the electrical parameters were measured at both stations, with remarkable differences between the two locations. While at the Mt. Hermon station we registered positive values of the electric field and total current density, the values registered at the Wise Observatory were significantly smaller and more negative. The Mt. Hermon site showed Ez and J values fluctuating between −460 and +570Vm−1 and −14.5 and +18pAm−2 respectively. In contrast, the Ez values registered at WO varied between −430 and +10Vm−1, and the current density fluctuated between −6 and +3pAm−2. We show that the unique generation and evolution of this dust outbreak gave rise to a significantly different charge structure compared with that observed in short lived convective events, and suggest a tentative explanation for the obtained results.

Automatized Photometric Monitoring of Active Galactic Nuclei with the 46 cm Telescope of the Wise Observatory

We present the first results of an ongoing variability monitoring program of active galactic nuclei (AGNs) using the 46 cm telescope of the Wise Observatory in Israel. The telescope has a field of view of and is specially equipped with five narrowband filters at 4300, 5200, 5700, 6200, and 7000 Å to perform photometric reverberation mapping studies of the central engine of AGNs. The program aims to observe a sample of 27 AGNs (V mag) selected according to tentative continuum and line time delay measurements obtained in previous works. We describe the autonomous operation of the telescope together with the fully automatic pipeline used to achieve high-performance unassisted observations, data reduction, and light curves extraction using different photometric methods. The science verification data presented here demonstrates the performance of the monitoring program in particular for efficiently photometric reverberation mapping of AGNs with additional capabilities to carry out complementary studies of other transient and variable phenomena such as variable stars studies.

The eShel Spectrograph: A Radial-velocity Tool at the Wise Observatory

The eShel, an off-the-shelf, fiber-fed echelle spectrograph (), was installed on the 1 m telescope at the Wise observatory in Israel. We report the installation of the multi-order spectrograph, and describe our pipeline to extract stellar radial velocity from the obtained spectra. We also introduce a new algorithm—UNICOR, to remove radial-velocity systematics that can appear in some of the observed orders. We show that the system performance is close to the photon-noise limit for exposures with more than 107 counts, with a precision that can get better than 200 m s−1 for F–K stars, for which the eShel spectral response is optimal. This makes the eShel at Wise a useful tool for studying spectroscopic binaries brighter than mV = 11. We demonstrate this capability with orbital solutions of two binaries from projects being performed at Wise.

An electrified dust storm over the Negev desert, Israel

We report on atmospheric electrical measurements conducted at the Wise Observatory in Mitzpe-Ramon, Israel (30°35′N, 34°45′E) during a large dust storm that occurred over the Eastern Mediterranean region on 10–11 February 2015. The dust was transported from the Sahara, Egypt and the Sinai Peninsula ahead of an approaching Cyprus low. Satellite images show the dust plume covering the Negev desert and Southern Israel and moving north. The concentrations of PM10 particles measured by the air-quality monitoring network of the Israeli Ministry of the Environment in Beer-Sheba reached values >450μgm−3 and the AOT from the AERONET station in Sde-Boker was 1.5 on February 10th. The gradual intensification of the event reached peak concentrations on February 11th of over 1200μgm−3 and an AOT of 1.8. Continuous measurements of the fair weather vertical electric field (Ez) and vertical current density (Jz) were conducted at the Wise Observatory with 1minute temporal resolution. Meteorological data was also recorded at the site. As the dust was advected over the observatory, very large fluctuations in the electrical parameters were registered. From the onset of the dust storm, the Ez values changed between +1000 and +8000Vm−1 while the current density fluctuated between −10pAm2 and +20pAm2, both on time-scales of a few minutes. These values are significant departures from the average fair-weather values measured at the site, which are ~−200Vm−1 and ~2pAm2. The disturbed episodes lasted for several hours on February 10th and the 11th and coincided with local meteorological conditions related to the wind speed and direction, which carried large amounts of dust particles over our observation station. We interpret the rapid changes as caused by the transport of electrically charged dust, carrying an excess of negative charge at lower altitudes.

Improving identification of weak spectral lines in the presence of a strong continuum

Observing faint spectral signals from light sources in the presence of an overwhelming background is a common goal in many aspects of physics and astronomy. By using an optimized selected part of a Fourier interferogram, we demonstrate that observability of such faint signals can be much improved. We present astronomical observations, in an on-sky experiment, made on several spectral types of star using a breadboard common path scanless interferometer on the Wise Observatory 1m telescope. We obtain an improvement of signal-to-background of up to 35 for a given exposure time.

Faint extended structures near galaxies: preliminary results from the Wise Observatory

AbstractWe present the first results from a survey of deep imaging of edge-on galaxies, with the goal of testing the growth-by-accretion of galaxies proposed by ΛCDM. The data were obtained with a new telescope at the Wise Observatory. Our images show previously unreported extensions of the disk, tidal distortions, and streams at the level of 27-28 mag arcsec−2.

SEARCH FOR LOW-MASS OBJECTS IN THE GLOBULAR CLUSTER M4. I. DETECTION OF VARIABLE STARS

ABSTRACT With every new discovery of an extrasolar planet, the absence of planets in globular clusters (GCs) becomes more and more conspicuous. Null detection of transiting hot Jupiters in GCs 47 Tuc, ω Cen, and NGC 6397 presents an important puzzle, raising questions about the role played by cluster metallicity and environment on formation and survival of planetary systems in densely populated stellar clusters. GCs were postulated to have many free-floating planets, for which microlensing (ML) is an established tool for detection. Dense environments, well-constrained distances and kinematics of lenses and sources, and photometry of thousands of stars simultaneously make GCs the ideal targets to search for ML. We present first results of a multisite, 69-night-long campaign to search for ML signatures of low-mass objects in the GC M4, which was chosen because of its proximity, location, and the actual existence of a planet. M4 was observed in R and I bands by two telescopes, 1 m T40 and 18-inch C18, of the Wise Observatory, Tel Aviv, Israel, from 2011 April to July. Observations on the 1 m telescope were carried out in service mode, gathering 12 to 48 20 s exposures per night for a total of 69 nights. C18 observations were done for about 4 hr a night for six nights in 2011 May. We employ a semiautomated pipeline to calibrate and reduce the images to the light curves that our group is developing for this purpose, which includes the differential photometry package DIAPL, written by Wozniak and modified by W. Pych. Several different diagnostics are employed for search of variability/transients. While no high-significance ML event was found in this observational run, we have detected more than 20 new variables and variable candidates in the M4 field, which we present here.

Galaxy interactions in the Hickson Compact Group 88

I present observations of the Hickson Compact Group 88 (HCG88) obtained during the commissioning of a new 28-inch telescope at the Wise Observatory. This galaxy group was advertized to be non-interacting, or to be in a very early interaction stage, but this is not the case. The observations reported here were done using a ‘luminance’ filter, essentially a very broad R filter, reaching a low surface brightness level of ≈26 mag arcsec−2. Additional observations were obtained in a narrow spectral band approximately centred on the rest-frame H α line from the group. Contrary to previous studies, my observations show that at least two of the major galaxies have had significant interactions in the past, although probably not between themselves. I report the discovery of a faint extended tail emerging from the brightest of the group galaxies, severe isophote twisting and possible outer shells around another galaxy, and map the H ii regions in all the galaxies.

The Jay Baum Rich telescope: a Centurion 28 at the Wise Observatory

We describe the third telescope of the Wise Observatory, a 0.70-m Centurion 28 (C28IL) installed in 2013 and named the Jay Baum Rich telescope to enhance significantly the wide-field imaging possibilities of the observatory. The telescope operates from a 5.5-m diameter dome and is equipped with a large-format red-sensitive CCD camera, offering a ~one square degree imaged field sampled at 0".83/pixel. The telescope was acquired to provide an alternative to the existing 1-m telescope for studies such as microlensing, photometry of transiting exo-planets, the follow-up of supernovae and other optical transients, and the detection of very low surface brightness extended features around galaxies. The operation of the C28IL is robotic, requiring only the creation of a night observing plan that is loaded in the afternoon prior to the observations. The entire facility was erected for a component and infrastructure cost of well under 300k$ and a labor investment of about two person-year. The successful implementation of the C28IL, at a reasonable cost, demonstrates the viability of small telescopes in an age of huge light-collectors.

An optical-UV-IR survey of the North Celestial Cap – I. The catalogue

We describe the final product of the North Celestial Cap Survey (NCC Survey, NCCS) - the optical-UV-IR merged catalogue for the region within 10 deg of the North Celestial Pole. The NCC region at DEC > 80 deg is poorly covered by modern CCD-based surveys. The optical part of the survey was observed in V, R and I with the Wise Observatory telescopes and was merged with GALEX UV and WISE IR data, producing the catalogue. More than four million objects were observed in at least one optical band. The final catalogue contains ~1.6 million sources observed in all three optical bands, of which some 1.4 million have WISE counterparts and ~300,000 have GALEX counterparts. The astrometric accuracy of the optical NCCS data, derived from a comparison with the UCAC3 catalogue, is better than 0.2 arcsec and the photometry, when compared with SDSS, is good to ~0.15 mag for sources brighter than V = 20.3, R = 21.0 and I = 19.2 mag. The SDSS point-extended source separation is reproduced with >92% efficiency.

Broad-line region structure and kinematics in the radio galaxy 3C 120

Broad emission lines originate in the surroundings of supermassive black holes in the centers of active galactic nuclei (AGN). One method to investigate the extent, structure, and kinematics of the BLR is to study the continuum and line profile variability in AGN. We selected the radio-loud Seyfert 1 galaxy 3C 120 as a target for this study. We took spectra with a high signal-to-noise ratio of 3C 120 with the 9.2m Hobby-Eberly Telescope between Sept. 2008 and March 2009. In parallel, we photometrically monitored the continuum flux at the Wise observatory. We analyzed the continuum and line profile variations in detail (1D and 2D reverberation mapping) and modeled the geometry of the line-emitting regions based on the line profiles. We show that the BLR in 3C 120 is stratified with respect to the distance of the line-emitting regions from the center with respect to the line widths (FWHM) of the rms profiles and with respect to the variability amplitude of the emission lines. The emission line wings of H{\alpha} and H{\beta} respond much faster than their central region. This is explained by accretion disk models. In addition, these lines show a stronger response in the red wings. However, the velocity-delay maps of the helium lines show a stronger response in the blue wing. Furthermore, the HeII{\lambda}4686 line responds faster in the blue wing in contradiction to observations made one and a half years later when the galaxy was in a lower state. The faster response in the blue wing is an indication for central outflow motions when this galaxy was in a bright state during our observations. The vertical BLR structure in 3C 120 coincides with that of other AGN. We confirm the general trend: the emission lines of narrow line AGN originate at larger distances from the midplane than AGN with broader emission lines.