Magnetic cycles of Sun-like stars with different levels of coronal and chromospheric activity——comparison with the Sun

The atmospheric activity of the Sun and Sun-like stars is analyzed involving observations from the HK-project at the Mount Wilson Observatory, the California and Carnegie Planet Search Program at the Keck and Lick Observatories and the Magellan Planet Search Program at the Las Campanas Observatory.We show that for stars of F, G and K spectral classes, the cyclic activity, similar to the 11-yr solar cycle, is different: it becomes more prominent in K-stars. Comparative study of Sun-like stars with different levels of chromospheric and coronal activity confirms that the Sun belongs to stars with a low level of chromospheric activity and stands apart among these stars by its minimum level of coronal radiation and minimum level of variations in photospheric flux.     

Correlation of He II lyman alpha with He I 10830 Å, and with chromospheric and EUV coronal emission

This paper describes the results of comparing SERTS-3 images obtained in the transition region line of Heii 304 with chromospheric Hei 10830 absorption, with strong coronal lines of Mgix 368 , Fexv 284 and 417 , and Fexvi 335 and 31 , with H, with Caii 8542 , and with magnetograms in Fei 8688H. All of the images are illustrated, and the image reconstruction techniques used are described and evaluated. The high correlation of the Heii 304 and Hei 10830 images, originally found by Harvey and Sheeley (1977), is confirmed and is put on a quantitative basis. We find that the supergranulation network has greater contrast, and that filaments appear darker, in 10830 than in 304 . In active regions, the 304 line follows more closely the behavior of H and Caii 8542 than the 10830 line.     

Martian “microfossils” in lunar meteorites?

Abstract— One of the five lines of evidence used by McKay et al. (1996) for relic life in the Martian meteorite Allan Hills (ALH) 84001 was the presence of objects thought to be microfossils. These ovoid and elongated forms are similar to structures found in terrestrial rocks and described as “nanobacteria” (Folk, 1993; McBride et al, 1994). Using the same procedures and apparatus as McKay et al. (1996), we have found structures on internal fracture surfaces of lunar meteorites that cannot be distinguished from the objects described on similar surfaces in ALH 84001. The lunar surface is currently a sterile environment and probably always has been. However, the lunar and Martian meteorites share a common terrestrial history, which includes many thousands of years of exposure to Antarctic weathering. Although we do not know the origin of these ovoid and elongated forms, we suggest that their presence on lunar meteorites indicates that the objects described by McKay et al. (1996) are not of Martian biological origin.     

A magnetic core in the Sun? The solar rotator

The previously found solar distortion rotating rigidly and wave-like on the surface with a 12 day period is interpreted as the shape of the gravitational potential induced by the solar core distorted by an internal magnetic field and rotating rigidly with this period. The distortion does not have a symmetry axis and the necessary magnetic field is not compatible with the axial symmetry required of a quasi-static field locked in the rotating core. It is concluded that if the solar distortion is due to such a process the core is oscillating with a very long period, a toroidal oscillation with a period of the order of years.This research was supported in part by the National Science Foundation.     

Is the “astrometric” plate reduction method rigorous?

It is shown that there is no intrinsic difference between the so-called “astrometric” and “photogrammetric” methods of reducing star plates, and that either, when applied by competent investigators, will yield equivalent results.     

The exceptionally hot summer of 2007 in Athens, Greece — A typical summer in the future climate?

Summer 2007 was abnormally warm for many areas of southeastern Europe, the Balkan peninsula and parts of Asia Minor with departures from the seasonal means exceeding 4 °C in some areas but also distinct periods of extremely hot weather. Greece experienced very likely the warmest summer of its instrumental history with record breaking temperatures being observed at a number of stations. The historical air temperature record of the National Observatory of Athens (NOA), extending back to the 19th century, was used in order to highlight the rarity of the event. Seasonal (June to August) temperature anomalies at NOA exceeded 3 °C corresponding to more than 3 standard deviations with respect to the 1961–1990 reference period. The record value of 44.8 °C was observed at NOA on 26 June 2007 (previous record 43 °C in June 1916) during the first and most intense heat wave that affected the area. The study places summer 2007 in the climatology of the previous century and also examines whether the statistics of summer 2007 have similarities with Mediterranean summers of the future. An ensemble of regional climate model simulations undertaken for the European domain indicate that summer 2007 reflects the daily maximum temperatures that are projected to occur in the latter part of the 21st century. The analysis of temperature data from other less urbanized stations indicates that the urban heat effect in Athens contributed positively to the anomalies of the nocturnal temperatures. The abnormally hot summer of 2007 is perhaps not the proof but a strong indicator of what eastern Mediterranean summers could resemble in future.     

The global distribution of pyroclastic deposits on Mercury: The view from MESSENGER flybys 1–3

We present a global survey of candidate pyroclastic deposits on Mercury, derived from images obtained during MESSENGER flybys 1–3 that provided near-global coverage at resolutions between 5 and 0.5 km/pixel. Thirty-five deposits were identified and characterized and are located principally on the floors of craters, along rims of craters, and along the edge of the Caloris basin. Deposits are commonly centered on rimless, often irregularly shaped pits, mostly between 5 and 45 km in diameter. The deposits identified are generally similar in morphology and absolute reflectance to lunar pyroclastic deposits. Spectrally the deposits appear brighter and redder than background Mercury terrain. On the basis of the available coverage, the candidate pyroclastic deposits appear to be essentially globally distributed. The diameters of the deposits, when mapped to lunar gravity conditions, are larger than their lunar counterparts, implying that more abundant volatiles were present during the typical eruptive process than on the Moon. These observations indicate that if these deposits resulted from hawaiian-style eruptions, the volatile contents required would be between ～1600 and 16,000 ppm CO or an equivalent value of H₂O, CO₂, SO₂, or H₂S (for a more oxidizing interior), or N₂, S₂, CS₂, S₂Cl, Cl, Cl₂, or COS (for a more reducing interior). These abundances are much greater than those predicted by existing models for Mercury's formation. An apparent lack of small deposits, compared with the Moon, may be due to resolution effects, a topic that can be further assessed during the orbital phase of the MESSENGER mission. These results provide a framework within which orbital observations by MESSENGER and the future BepiColombo mission can be analyzed.     

“Pathological” Martian craters: Evidence for a transient obliteration event?

Abstract— We have detected three unusual, low-relief circular features, 1.2 to 2.1 km in diameter, in the northwest Noachis highlands, which may be craters that have undergone isostatic deformation. They may shed light on the existence, nature, and timing of suspected widespread Martian erosion/obliteration events, and offer clues to a type of Martian terrain softening. In the surrounding area, we find an anomalous deficiency of craters in the 3–11 km diameter range and evidence that larger, older craters have undergone relief softening and infill. We discuss three different hypotheses to explain these features, two of which involve Martian ice. This region may have undergone a transient event in which a near-surface permafrost layer (several hundred meters deep) underwent partial melting or softening. This would allow relaxation of kilometer-scale craters and softening of larger craters. Crater data presented here suggest that this event happened some time in mid-Martian history. Whether the event was regional or related to global-scale events is uncertain, though it may represent a class of events that also happened in other Martian areas.     

The characteristics of the coronal mass ejections preceding the associated X-ray and γ-ray burst solar flares

In this study, investigated 14,786 coronal mass ejection (CME) events and 5092 Gamma-ray Burst Monitor (GBM) solar flare events (called γ-ray burst solar flare) recorded during 2008–2017, by using temporal and spatial conditions criteria, we found 845 (about 16%) CME events associated with γ-ray burst solar flare events only (hereafter, CME–γ-preflare). All the 845 events are associated with solar flares that are detected in both GBM and RHESSI simultaneously. Investigating the characteristics of these events, we found that the best time interval is 0–2 h before the flare's start time. The mean time interval for these CME–γ-preflare associated events is 61 min, with the flare's duration mean value of 12 min, which is greater than non-associated γ-ray solar flare's duration. CME width of CME-γ-preflare associated events 64° is slightly wider and slightly faster (remain lower than solar wind's speed) than non-associated CME 53°.     

Microvariability of spectral line profiles and magnetic fields of early-type stars: <Emphasis Type="Italic">ζ</Emphasis> Ori A

We report the results of spectropolarimetric observations of the supergiant ζ Ori A made with 6-m BTA telescope of the SAO RAS. We found regular variations of line profiles in the spectrum of the star with a period of 1–3 hours and point to their possible association with nonradial photospheric pulsations. We also searched for a possible weak magnetic field in ζ Ori A, but observations did not confirm the existence of such a field in the star considered.     

The rings of saturn: A frost-coated semiconductor?

Optical complex indices of refraction for the iron-sulfur semiconductors troilite and pyrrhotite have been measured between 0.3 and 1.1 μm, and at 1.5 and 3.0 cm in the microwave region. The behavior of the absorptive and refractive components of the index in the visual and ultraviolet regions suggests a reasonable match to published data on Saturn's rings. A combination of the iron sulfur with water ice and the orthopyroxene enstatite is consistent with an equilibrium condensation model for the formation of the solar system; the water ice and an orthopyroxene are also suggested by near-infrared observational data. A combination of these materials could explain all spectral features seen in the ring spectra to date. The microwave behavior of a small quantity of troilite embedded in water ice at low temperatures is consistent with the radar reflectivity and radio emissivity data.     

The existence of long-lived rays of the coronal streamer belt – Radial density and velocity distributions of the solar wind flowing in them

A technique is proposed for separating the rays of the streamer belt with quasi-stationary and non-stationary solar wind (SW) flows. It is shown that the lifetime of rays with a quasi-stationary SW can exceed 20 days. A new method has been developed for measuring the relative density distribution of a quasi-stationary slow SW flowing along the streamer belt's ray of increased brightness, based on the LASCO/SOHO data. It is shown that the density n for such SW flows varies with the radius R according to the relationship nR ^–, where =₁3.3–3.9 within 4 R ₀ R 6 R ₀ (here R ₀ is the solar radius), and decreases gradually further away. It is also shown that the V(R)-profiles in some rays of the streamer belt differ little from each other, although the value of the mass flow density, j _E, at the Earth's orbit in them can vary more than by a factor of 4. This distinguishes in a crucial respect a slow SW in the streamer belt's rays from a fast SW originating in coronal holes, for which j _Econstant and the dependences V(R) in different fast flows can differ greatly.     

The Precursor of GRB211211A:A Tide-induced Giant Quake?

The equilibrium configuration of a solid strange star in the final inspiral phase with another compact object is generally discussed,and the starquake-related issue is revisited,for a special purpose to understand the precursor emission of binary compact star merger events(e.g.,that of GRB211211A).As the binary system inspirals inward due to gravitational wave radiation,the ellipticity of the solid strangeon star increases due to the growing tidal field of its compact companion.Elastic energy is...     

STELLA and RoboTel – a prototype for a robotic network?

Robotic telescopes are more and more commonly used in today's astronomical research. In fact, several facilities are spread around the globe, already forming a loose net. A big leap forward would lie in the capabilities to share observations between different telescopes. One gains immediately weather independence and the possibility of continuous observations from a working network. In this paper, the three robotic telescope operated under the hood of the Astrophysical Institute Potsdam are introduced, the potential of a robotic telescope network are sketched out and principle hints on accomplishing such a network are outlined. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The magnetic geometry and structure of the giant post-flare arch of 21–22 May, 1980

On 21–22 May, 1980 the HXIS instrument aboard SMM imaged an enormous, more-or-less stationary, X-ray arch structure near the position of a large two-ribbon flare which immediately preceded it in time. As described by vestka et al. (1982), the arch remained visible for up to 10 hours. Previous inferences of the height, orientation, and physical parameters of this feature have been based largely on the X-ray data and on radio observations of the associated stationary Type I noise storm. In the present paper we use the observed photospheric line-of-sight magnetic field distribution to compute, in the current-free approximation, the three-dimensional topology of the coronal field above the flare site. Comparing the HXIS intensity contours of the arch to the projected shapes of the field lines suggests that the arch is indeed aligned with certain coronal flux tubes and allows an independent determination of the geometrical arch parameters to be made. This procedure indicates that the true height of the arch is about 70000 km, i.e., appreciably less than was suggested previously (although it is still certainly to be classified as a giant feature of the post-flare evolution).These results suggest that the arch may be a by-product of magnetic reconnection occurring far above the flare site, analogous to the post-flare loops seen at lower heights. Unlike the latter, however, the field lines undergoing reconnection here link more distant parts of the active region; i.e., they do not represent direct linkages across the magnetic neutral line and thus appear to be topologically quite distinct from those which thread the underlying post-flare loops. In fact, of this group of peripheral field lines, the arch could simply comprise the lowest-lying ones to have been opened up by the flare process (and the first to reconnect again). This would explain why both the arch and the post-flare loops were visible early in the decay phase, being products of separate reconnection processes. Moreover, because of the lower plasma density and longer cooling times of the arch, this feature persisted long after the post-flare loops faded from view. A calculation of the magnetic energy liberated by reconnection shows that this process is easily capable of satisfying the overall energy requirements of the arch (the latter as determined from observations).On leave from Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A.     

The Swift Ultra-Violet/Optical Telescope: a view of today and tomorrow

Currently there are four operating near-UV imaging space telescopes, one of which is the Swift Ultra-Violet/Optical Telescope (UVOT). Although the UVOT was primarily built for observations of γ-ray bursts, it has become a powerful instrument for studying other types of UV and optical astronomical phenomena. Here we discuss the properties of the UVOT, summarize some of the science undertaken with the UVOT, and present other possible science goals for the UVOT that have not yet been pursued. We also discuss some lessons learned that apply to future UV telescopes.     

A Model of The 2–4 μm Spectrum of Comet Halley

Recent observations of Halley's Comet show a broad absorption band centred at 3.4 μm and which can be explained on the basis of a bacterial grain model. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the large-scale diffuse magnetic field of the Sun – II. The Contribution of Active Regions

Dikpati and Choudhuri (1994, 1995) developed a model for the poleward migration of the weak diffuse magnetic field on the Sun's surface. This field was identified with the poloidal component produced by the solar dynamo operating at the base of the convection zone, and its evolution was studied by considering the effects of meridional circulation and turbulent diffusion. The earlier model is extended in this paper by incorporating the flux from, the decay of tilted active regions near the solar surface as an additional source of the poloidal field. This extended model can now explain various low-latitude features in the time-latitude diagram of the weak diffuse fields. These low-latitude features could not be accounted for in the earlier model, which was very successful in modeling the behavior at high latitudes. The time-latitude diagrams show that regions of a particular polarity often have tongues of opposite polarity. Such tongues can be produced in the theoretical model by incorporating fluctuations in the source term arising out of the decaying active regions.