Coronae Borealis Research Articles

Magnetic field topology of the cool, active, short-period binary system σ2 Coronae Borealis

Aims. The goal of this work is to study the cool, active binary star σ2 CrB, focussing on its magnetic field. The two F9–G0 components of this system are tidally locked and in a close orbit, increasing the chance of interaction between their magnetospheres. Methods. We used Stokes IV data from the twin spectropolarimeters Narval at the TBL and ESPaDOnS at the CFHT. The least-squares deconvolution multi-line technique was used to increase the signal-to-noise ratio of the data. We then applied a new binary Zeeman–Doppler imaging code to reconstruct simultaneously the magnetic topology and brightness distribution of both components of σ2 CrB. This analysis was carried out for two observational epochs in 2014 and 2017. Results. A previously unconfirmed magnetic field of the primary star has been securely detected. At the same time, the polarisation signatures of the secondary appear to have a systematically larger amplitude than that of the primary. This corresponds to a stronger magnetic field, for which the magnetic energy of the secondary exceeds that of the primary by a factor of 3.3–5.7. While the magnetic energy is similar for the secondary star in the two epochs, the magnetic energy is about twice as high in 2017 for the primary. The magnetic field topology of the two stars in the earlier epoch (2014) is very different. The fractions of energy in the dipole and quadrupole components of the secondary are similar and thereafter decrease with increasing harmonic angular degree ℓ. At the same time, for the primary the fraction of energy in the dipole component is low and the maximum energy contribution comes from ℓ = 4. However, in the 2017 epoch both stars have similar field topologies and a systematically decreasing energy with increasing ℓ. In the earlier epoch, the magnetic field at the visible pole appears to be of opposite polarity for the primary and secondary, suggesting linked magnetospheres. The apparent rotational periods of both σ2 CrB components are longer than the orbital period, which we interpret as an evidence of a solar-like differential rotation. Conclusions. Despite their nearly identical fundamental parameters, the components of σ2 CrB system exhibit different magnetic field properties. This indicates that the magnetic dynamo process is a very sensitive function of stellar parameters.

Are DY Persei Stars Cooler Cousins of R Coronae Borealis Stars?

Abstract In this paper we present, for the first time, the study of low resolution H- and K-band spectra of 7 DY Per type and suspect stars, as well as DY Persei itself. We also observed H- and K-band spectra of 3 R Coronae Borealis (RCB) stars, 1 hydrogen-deficient carbon (HdC) star, and 14 cool carbon stars, including normal giants as comparisons. High 12C/13C and low 16O/18O ratios are characteristic features of majority RCBs and HdCs. We have estimated 16O/18O ratios of the program stars from the relative strengths of the 12C16O and 12C18O molecular bands observed in K-band. Our preliminary analysis suggests that a quartet of the DY Per suspects, along with DY Persei itself, seem to show isotopic ratio strength consistent with that of RCB/HdC stars, whereas two of them do not show significant 13C and 18O in their atmospheres. Our analysis provides further indications that DY Per type stars could be related to the RCB/HdC class of stars.

Unidentified emission features in the R Coronae Borealis star V854 Centauri

During its 2012 decline, the R Coronae Borealis star (RCB) V854 Cen was spectroscopically monitored with X-shooter on the ESO Very Large Telescope. The obscured optical and near-infrared spectrum exhibits many narrow and several broad emission features, as previously observed. The envelope is spatially resolved along the slit and allows for a detailed study of the circumstellar material. In this Letter, we report on the properties of a number of unidentified visual emission features (UFs), including the detection of a new feature at 8692 Å. These UFs have been observed in the Red Rectangle (RR), but their chemical and physical nature is still a mystery. The previously known UFs behave similarly in the RR and in V854 Cen, but are not detected in six other observed RCBs. Some hydrogen might be required for the formation of their carrier(s). The λ8692 UF is present in all RCBs. Its carrier is likely of a carbonaceous molecular nature, presumably different from that of the other UFs.

Erratum: “Peculiar Motions of Galaxy Clusters in the Regions of the Corona Borealis, Bootes, Z 5029/A 1424, A1190, A1750/A 1809 Superclusters of Galaxies”

We present results of the study of peculiar motions of 57 clusters and groups of galaxies in the regions of the Corona Borealis (CrB), Bootes (Boo), Z5029/A1424, A1190, A1750/A1809 superclusters of galaxies and the galaxy clusters located beyond massive structures (0.05 < z < 0.10). Using the SDSS (Data Release 8) data, a sample of early-type galaxies was compiled in the systems under study, their fundamental planes were built, and relative distances and peculiar velocities were determined. Within the galaxy superclusters, significant peculiar motions along the line of sight are observed with rms deviations of 652 ± 50 kms−1—in CrB, 757 ± 70 kms−1—in Boo. In the most massive A2065 cluster in the CrB supercluster, no peculiar velocity was found. Peculiar motions of the other galaxy clusters can be caused by their gravitational interaction both with A2065 and with the A2142 supercluster. It has been found that there are two superclusters projected onto each other in the region of the Bootes supercluster with a radial velocity difference of about 4000 kms−1. In the Z 5029/A1424 supercluster near the rich Z5029 cluster, the most considerable peculiar motions with a rms deviations of 1366 ± 170 kms−1 are observed. The rms deviations of peculiar velocities of 20 clusters that do not belong to large-scale structures is equal to 0 ± 20 kms−1. The whole sample of the clusters under study has the mean peculiar velocity equal to 83 ± 130 kms−1 relative to the cosmic microwave background.

SYMBOLISM OF THE "CROWN" - BETWEEN HEAVEN AND EARTH

From the cycle of the constellation symbolism we will approach the „Corona-Crown” constellation. The origin of these dress accessories gets lost in the darkness of time, standing testimony of the „Prehistoric Art”. The "Corona- Crown" is the small constellation Corona Borealis, visible in early summer, its brightest stars form a semicircular arc. The "crown" is a symbol and sign of belonging to the celestial world bearer, supernatural, divine, being worn at rituals of passage; of magic; of gratitude to heroes, to victors, to geniuses and to wise; of martyrdom; of coronation of kings, being a sign of immortality, honor, victory, greatness and joy. Archaeological discoveries will complete the mythological and ritualistic picture of these hairy ornaments, represented by „Moon Goddess” from Turdaș and „Bride of Trușești”. The story behind these clothing accessories represented in the Prehistoric Art and in the stars makes that the man to be closer to sky (heaven, deity), the microcosmic Earth merging with the macrocosmic Universe.

Peculiar motions of galaxy clusters in the regions of the Corona Borealis, Bootes, Z 5029/A 1424, A 1190, A 1750/A 1809 superclusters of galaxies

We present results of the study of peculiar motions of 57 clusters and groups of galaxies in the regions of the Corona Borealis (CrB), Bootes (Boo), Z5029/A1424, A1190, A1750/A1809 superclusters of galaxies and 20 galaxy clusters located beyond massive structures ($0.05<z<0.10$). Using the SDSS (Data Release 8) data, a sample of early-type galaxies was compiled in the systems under study, their fundamental planes were built, and relative distances and peculiar velocities were determined. Within the galaxy superclusters, significant peculiar motions along the line of sight are observed with rms deviations of $652\pm50$~km s$^{-1}$---in CrB, $757\pm70$~km s$^{-1}$---in Boo. For the most massive A2065 cluster in the CrB supercluster, no peculiar velocity was found. Peculiar motions of other galaxy clusters can be caused by their gravitational interaction both with A\,2065 and with the A2142 supercluster. It has been found that there are two superclusters projected onto each other in the region of the Bootes supercluster with a radial velocity difference of about 4000~km s$^{-1}$. In the Z5029/A1424 supercluster near the rich Z5029 cluster, the most considerable peculiar motions with a rms deviation of $1366\pm170$~km s$^{-1}$ are observed. The rms deviation of peculiar velocities of 20 clusters that do not belong to large-scale structures is equal to $0\pm20$~km s$^{-1}$. The whole sample of the clusters under study has the mean peculiar velocity equal to $83\pm130$~km s$^{-1}$ relative to the cosmic microwave background.

Abundance Analyses of the New R Coronae Borealis Stars ASAS-RCB-8 and ASAS-RCB-10

Abundance analyses of the two newly discovered R Coronae Borealis (RCB) stars ASAS-RCB-8 and ASAS-RCB-10 were conducted using high-resolution optical spectra and model atmospheres. Their chemical compositions place the pair among the majority class of RCBs. ASAS-RCB-10 is one of the most N-poor majority RCBs with an above average O abundance. Relative to ASAS-RCB-10, ASAS-RCB-8 is H poor by 1.6 dex, O-poor by 0.7 dex but N-rich by 0.8 dex suggesting a higher contamination by CNO-cycled material.

Evolution of galaxy groups

We study the variations of the properties of groups of galaxies with dynamical masses of 1013 M ⊙<M 200<1014 M ⊙, represented by two samples: one has redshifts of z 0.027, and is located in the regions of the following superclusters of galaxies: Hercules, Leo, Bootes, Ursa Major, and Corona Borealis. Using the archived data of the SDSS and 2MASX catalogs, we determined the concentration of galaxies in the systems by measuring it as the inner density of the group within the distance of the fifth closest galaxy from the center brighter than M K = −23. m 3. We also measured the magnitude gap between the first and the fourth brightest galaxies ΔM 14 located within one half of the selected radius R 200, the fraction of early-type galaxies, and the ratio of bright dwarf galaxies (Mr = [−18. m 5,−16. m 5]) to giant galaxies (M r < −18. m 5) (DGR) within the radius R 200. The main aim of the investigation is to find among these characteristics the ones that reflect the evolution of groups of galaxies.We determined that the ratio of bright dwarf galaxies to early-type giant galaxies on the red sequence depends only on the x-ray luminosity: the DGR increases with luminosity. The fraction of early-type galaxies in the considered systems is equal, on average, to 0.65 ± 0.01, and varies significantly for galaxies with σ200 < 300 kms−1. Based on the luminosity of the brightest galaxy, the magnitude gap between the first and the fourth brightest galaxies in the groups, and on model computations of these parameters, we selected four fossil group candidates: AWM4, NGC0533, NGC0741, and NGC6098 (where the brightest galaxy is a double).We observe no increase in the number of faint galaxies (the α parameter of the Schechter function is less than 1) in our composite luminosity function (LF) for galaxy systems with z < 0.027 in the M K = [−26m,−21. m 5] range, whereas earlier we obtained α > 1 for the LF of the Hercules and Leo superclusters of galaxies.

Disappearance and Displacement: The San, the Bamangwato, and the British in the Bechuanaland Protectorate, 1943–1945

One of the enduring historical mysteries of the Kalahari Desert of Southern Africa is that of the disappearance of two Royal Air Force cadets during the Second World War. Eight Tshwa San (Bushmen) were arrested and tried for the murder of the flyers. The trial took place in the High Court of the Bechuanaland Protectorate (BP) in September to October, 1944, and resulted in a verdict of not guilty. Despite their exoneration, repercussions followed for the San. These included the resettlement of those who had been acquitted and their families, followed by the intentional displacement of hundreds of other Tshwa San from their traditional homelands in the Northern Crown Lands region of Bechuanaland. This paper explores the circumstances under which the RAF flyers disappeared and assesses the complex interactions among the San, the Bamangwato, and the British in 1943 and the years following. It also addresses the colonial perceptions, prejudices, and cultural misunderstandings that led to the large-scale displacement and the impacts of these events on Southern African peoples and states.

Investigation of Faint Galactic Carbon Stars from the First Byurakan Spectral Sky Survey. III. Infrared Characteristics

Infra-Red(IR) astronomical databases, namely, IRAS, 2MASS, WISE, and Spitzer, are used to analyze photometric data of 126 carbon stars whose spectra are visible in the First Byurakan Survey low-resolution spectral plates. Among these, six new objects, recently confirmed on the digitized FBS plates, are included. For three of them, moderate-resolution CCD optical spectra are also presented. In this work several IR color-color diagrams are studied. Early and late-type C stars are separated in the JHK Near-Infra-Red(NIR) color-color plots, as well as in the WISE W3-W4 versus W1-W2 diagram. Late N-type Asymptotic Giant Branch stars are redder in W1-W2, while early-types(CH and R giants) are redder in W3-W4 as expected. Objects with W2-W3 > 1.0 mag. show double-peaked spectral energy distribution, indicating the existence of the circumstellar envelopes around them. 26 N-type stars have IRAS Point Source Catalog(PSC) associations. For FBS 1812+455 IRAS Low-Resolution Spectra in the wavelength range 7.7 - 22.6micron and Spitzer Space Telescope Spectra in the range 5 - 38micro are presented clearly showing absorption features of C2H2(acetylene) molecule at 7.5 and 13.7micron , and the SiC(silicone carbide) emission at 11.3micron. The mass-loss rates for eight Mira-type variables are derived from the K-[12] color and from the pulsation periods. The reddest object among the targets is N-type C star FBS 2213+421, which belong to the group of the cold post-AGB R Coronae Borealis(R CrB) variables.

New R Coronae Borealis and DY Persei Candidates in the SMC

We report 3 new R Coronae Borealis and 63 new DY Persei candidates in the Small Magellanic Cloud. Our analysis, based on data published by the OGLE team, consisted in a search for the characteristic drops in brightness that define these classes. All candidates had been previously classified as semi-regular or Mira variables. We briefly remark upon the possible existence of a "borderline" DY Per-like star and a "transitional" DY Per/RCB star. Follow-up observations are needed to conclusively establish the nature of our candidates.

A new search for R Coronae Borealis stars in the SMC

R Coronae Borealis (RCB) stars are rare, and their evolutionary origin is not well understood. Since they are obscured due to formation of carbon dust around the star during their mass loss events, RCB stars can be classified as self-eclipsing variable stars . The purpose of this work is to present a new search for RCB stars in the Small Magellanic Cloud (SMC), by analysing VI data from the OGLE project.

First four-color photometric investigation of extreme mass-ratio contact binary AS coronae borealis

The first high-precision BVRI light curves of the eclipsing binary AS CrB were presented and were analyzed by the 2015 version of the W-D code. It is found that AS CrB is an extreme mass-ratio, deep contact binary with a fill-out factor of f=59.6±2.5% and a mass ratio of q=0.172±0.008. Based on the photometric solution and the Dartmouth isochrones model, the masses, radii, and luminosities of the components are estimated as follows: M1=1.25±0.15M⊙,M2=0.21±0.06M⊙,R1=1.40±0.07R⊙,R2=0.67±0.04R⊙,L1=3.2±0.2L⊙, and L2=0.72±0.04L⊙, with an estimated distance 459 ± 42 pc. These uncertainties mainly come from the errors of the color used to estimate the temperature of the primary star. By investigating all of the available times of light minima, it is found that the Observed-Calculated [(O−C)] curve shows a long-term period increase, with a rate of dP/dt=+(3.46±0.01)×10−7 day/year. As an extreme mass-ratio contact binary, AS CrB may merge into a single star, such as an FK Com-type star or a blue straggler, because of the orbital instability.

Cosmic troublemakers: the Cold Spot, the Eridanus supervoid, and the Great Walls

The alignment of the CMB Cold Spot and the Eridanus supervoid suggests a physical connection between these two relatively rare objects. We use galaxy cata\-logues with photometric (2MPZ) and spectroscopic (6dF) redshift measurements, supplemented by low-redshift compilations of cosmic voids, in order to improve the 3D mapping of the matter density in the Eridanus constellation. We find evidence for a supervoid with a significant elongation in the line-of-sight, effectively spanning the total redshift range $z<0.3$. Our tomographic imaging reveals important substructure in the Eridanus supervoid, with a potential interpretation of a long, fully connected system of voids. We improve the analysis by extending the line-of-sight measurements into the antipodal direction that interestingly crosses the Northern Local Supervoid at the lowest redshifts. Then it intersects very rich superclusters like Hercules and Corona Borealis, in the region of the Coma and Sloan Great Walls, as a possible compensation for the large-scale matter deficit of Eridanus. We find that large-scale structure measurements are consistent with a central matter underdensity $\delta_0 \approx -0.25$, projected transverse radius $r_{0}^{\perp}\approx 195$ Mpc/h with an extra deepening in the centre, and line-of-sight radius $r_{0}^{\parallel}\approx500$ Mpc/h, i.e. an ellipsoidal supervoid. The expected integrated Sachs-Wolfe imprint of such an elongated supervoid is at the $\Delta T_{\rm ISW} \approx -40 \mu K$ level, thus inappropriate to accounting for the Cold Spot pattern in the CMB.

„Kiedy gwiazdy się na niebie złocą…” Metaforyka jubilerska w rzymskich opisach nieba

Metaphors and comparisons are typical features of the ancient texts describing celestial bodies, and they can be treated as a part of a broader cultural practice of seeking analogies between earth and sky phenomena, inspired by the microcosm/macrocosm theory. To explain such a practice we can refer to the modern theory of imagination as well, according to which appreciation of nature is based, among others, on the so-called “projective imagination”, transferring mentally the images from the terrestrial reality to the sky. One of the obvious instances of such an analogical thinking is “katasterismos”, mythic narration about the item placed in the heavens as a star or constellation. It appears that among the objects on the sky described as a result of “catasterism” we can find some specimens of jeweller’s craftsmanship (e.g. Ariadne’s Crown as Corona Borealis). This is, however, a specific situation; astronomical descriptions usually emphasize the brightness and perfection of the sky phenomena using above-mentioned poetic devices associated with jewellery. Most popular among them is the metaphoric epithet of “gold”, linked commonly with stars and the sun, but besides this, in the works of Roman authors can be detected more original imagery (e.g. the cosmos as a necklace). It is argued in the paper that this kind of astronomical descriptions can be interpreted against the backdrop of the history of the “visual metaphors of value”, as they were defined by Ernst Gombrich.

All known hot RCB stars are fading fast over the last century

The R Coronae Borealis (RCB) stars are cool supergiants that display irregular and deep dips in their light curves, caused by dust formation. There are four known hot RCB stars (DY Cen, MV Sgr, V348 Sgr, and HV 2671), with surface temperatures of 15,000--25,000 K, and prior work has suggested that three of these have secular fading in brightness. I have tested this result by measuring century-long light curves in the Johnson B-band with modern comparison star magnitudes, and I have extended this by measuring many magnitudes over a wide time range as well as for the fourth hot RCB star. In all four cases, the B-band magnitude of the maximum light is now fast fading. The fading rates (in units of magnitudes per century) are 2.5 for DY Cen after 1960, 1.3 for MV Sgr, 1.3 for V348 Sgr, and 0.7 for HV 2671. This secular fading is caused by the expected evolution of the star across the top of the HR diagram at constant luminosity, as the temperature rises and the bolometric correction changes. For DY Cen, the brightness at maximum light is rising from 1906 to 1932, and this is caused by the temperature increase from near 5,800 to 7,500 K. Before 1934 DY Cen had frequent dust dips, while after 1934 there are zero dust dips, so there is some apparent connection between the rising temperature and the formation of the dust. Thus, we have watched DY Cen evolve from an ordinary RCB star up to a hot RCB star and now appearing as an extreme helium star, all in under one century.

Does the Corona Borealis Supercluster form a giant binary-like system?

The distribution of local gravitational potentials generated by a complete volume-limited sample of galaxy groups and clusters filling the Corona Borealis region has been derived to search for new gravitational hints in the context of clus-tering analysis unrevealed by alternative methodologies. Mapping such a distribution as a function of spatial positions, the deepest potential wells in the sample trace unambiguously the locations of the densest galaxy cluster clumps providing the physical keys to bring out gravitational features connected to the formation, composition and evolution of the major clustered structures filling that region. As expected, the three deepest potential wells found at Equatorial coordinates: (~ 230{\deg}, ~ 28{\deg}, z ~ 0.075), (~ 240{\deg}, ~ 27{\deg}, z ~ 0.09) and, (227{\deg}, 5.8{\deg}, z ~ 0.0788) correspond to massive superclusters of galaxy groups and clusters identified as the Corona Borealis, A2142 and Virgo-Serpent, respectively. However, the deepest isopotential contours around the Corona Borealis and A2142 superclusters seem to suggest a gravitational feature similar to a giant binary-like system connected by a filamentary structure. To a first approximation, it seems unlikely that this hypothesized system could be gravitationally bound.

Shell-like structures in our cosmic neighbourhood

Signatures of the processes in the early Universe are imprinted in the cosmic web. Some of them may define shell-like structures characterised by typical scales. We search for shell-like structures in the distribution of nearby rich clusters of galaxies drawn from the SDSS DR8. We calculate the distance distributions between rich clusters of galaxies, and groups and clusters of various richness, look for the maxima in the distance distributions, and select candidates of shell-like structures. We analyse the space distribution of groups and clusters forming shell walls. We find six possible candidates of shell-like structures, in which galaxy clusters have maxima in the distance distribution to other galaxy groups and clusters at the distance of about 120 Mpc/h. The rich galaxy cluster A1795, the central cluster of the Bootes supercluster, has the highest maximum in the distance distribution of other groups and clusters around them at the distance of about 120 Mpc/h among our rich cluster sample, and another maximum at the distance of about 240 Mpc/h. The structures of galaxy systems causing the maxima at 120 Mpc/h form an almost complete shell of galaxy groups, clusters and superclusters. The richest systems in the nearby universe, the Sloan Great Wall, the Corona Borealis supercluster and the Ursa Major supercluster are among them. The probability that we obtain maxima like this from random distributions is lower than 0.001. Our results confirm that shell-like structures can be found in the distribution of nearby galaxies and their systems. The radii of the possible shells are larger than expected for a BAO shell (approximately 109 Mpc/h versus approximately 120 Mpc/h), and they are determined by very rich galaxy clusters and superclusters with high density contrast while BAO shells are barely seen in the galaxy distribution. We discuss possible consequences of these differences.

Distribution of Lepidopteran Larvae on Norway Spruce: Effects of Slope and Crown Aspect.

Lepidoptera associated with Norway spruce, Picea abies (L.) Karsten, play important roles in ecosystem processes, acting as plant pests, prey for predators, and hosts for parasites and parasitoids. Their distribution patterns in spruce crowns and forests are only poorly understood. We examined how slope and crown aspect affect the occurrence and abundance of moth larvae on solitary spruce trees in a montane region in Central Europe. Moth larvae were collected from southern and northern crowns of trees growing on south- and north-facing slopes (four treatments) using emergence boxes at the end of winter and by the beating method during the growing season. Species responses to slope and crown aspect were not uniform. Treatment effects on moth larvae were stronger in the winter than during the growing season. In winter, the abundance of bud-boring larvae was significantly higher in northern than in southern crowns regardless of the slope aspect, while both slope and aspect had marginally significant effects on abundance of miners. During the growing season, the occurrence of free-living larvae was similar among treatments. Emergence boxes and beating spruce branches are complementary techniques providing valuable insights into the assemblage structure of moth larvae on Norway spruce. Due to the uneven distribution of larvae detected in this study, we recommend adoption of a protocol that explicitly includes sampling of trees from contrasting slopes and branches from contrasting crown aspect in all seasons.

HubbleSpace Telescope ultraviolet spectroscopy of the hottest known helium-rich pre-white dwarf KPD 0005+5106

We present a model-atmosphere analysis of the ultraviolet echelle spectra of KPD 0005+5106 taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. The star is the hottest known pre-white dwarf (Teff = 200 000 ± 20 000 K, log g= 6.7 ± 0.3 (cm/s2)). Its atmosphere is composed of helium with trace amounts of metals. It is of the so-called O(He) spectral type that comprises very hot helium-rich pre-white dwarfs whose origin is debated. From neon and silicon ionisation balances, we derive tighter constraints on the effective temperature (195 000 ± 15 000 K) and improve previous abundance determinations of these elements. We confirm the idea that KPD 0005+5106 is the descendant of an R Coronae Borealis (RCB) star, so is the outcome of a binary-white-dwarf merger. We discuss the relation of KPD 0005+5106 to other O(He) and RCB stars.