The relationship between EUV dimming and coronal mass ejections

Aims. There have been many studies of extreme-ultraviolet (EUV) dimming in association with coronal mass ejection (CME) onsets. However, there has never been a thorough statistical study of this association, covering appropriate temperature ranges. Thus, we make use of a large campaign database utilising the Coronal Diagnostic Spectrometer (CDS) and the Large Angle and Spectrometric COronagraph (LASCO) both on the SOlar and Heliospheric Observatory (SOHO) to associate dimming events detected at 1 and 2 million K with CME activity. The aim is to confirm whether the dimming-CME association is real or not. This in turn will confirm whether special attention should be paid to the EUV dimming in the pre-eruption and eruption periods to study the CME onset process itself. Methods. The CDS CME onset campaign data for Mg IX and FE XVI observations on the solar limb are used to compare to LASCO event lists over a period from 1998 to 2005. Dimming events are identified and the physical extent explored, whilst comparing the events to overlying CME activity. Results. For the identified dimming regions we have shown strong associations with CME onsets, with up to 55% of the dimming events being associated with CME activity. This is compared to the random case where up to 47% of the dimming regions are expected to be associated with CMEs. We have also shown that up to 84% of CMEs associated with our data can be tracked back to dimming regions. This compares to a random case of up to 58%. Conclusions. These results confirm the CME-EUV dimming association, using a statistical analysis for the first time. We discuss the repercussions for the study of CME onsets, i.e. analysis of the dimming regions and the periods up to such dimming may be key to understanding the pre-CME onset plasma processes. The results stress that one emission line may not be sufficient for associating dimming regions with CMEs

Comparison of blinkers and explosive events:A case study

Blinkers are brightenings at network cell junctions that are traditionally identified with SOHO/CDS and explosive events or high velocity events are identified in high resolution UV spectra obtained from HRTS and SOHO/SUMER. Criteria are determined to facilitate objective automatic identification of both blinkers and explosive events in both SOHO/CDS and SOHO/SUMER data. Blinkers are identified in SUMER data, if the temporal resolution of the data is reduced to that of CDS. Otherwise short lived, localised intensity enhancements that make up the blinker are identified. Explosive events are identified in CDS data when the line width is significantly increased, and occasionally if there is an enhancement in the wing of the line profile. A theoretical statistical model is presented which hypothesises that blinkers and explosive events are random and not connected in any way. The results given in this paper suggest that this hypothesis can not be rejected and our probability interpretation of the recent results of Brković & Peter (2004, A&A, 422, 709) are inconclusive

Evidence for conservative mass transfer in the classical Algol system δ Librae from its surface carbon-to-nitrogen abundance ratio

Algol-type binary systems are the product of rapid mass transfer between the initially more massive component to its companion. It is still unknown whether the process is conservative, or whether substantial mass is lost from the system. The history of a system prior to mass exchange is imprinted in the photospheric chemical composition, in particular in the carbon-to-nitrogen (C/N) ratio. We use this to trace the efficiency of mass-transfer processes in the components of a classical Algol-type system, δ Librae. The present analysis is based on new spectroscopic data (ground-based high-resolution échelle spectra) and extracted archival photometric observations (space-based measurements from the STEREO satellites). In the orbital solution, non-Keplerian effects on the radial-velocity variations were taken into account. This reduces the primary’s mass by 1.1  M⊙ (∼23%) significantly in comparison to previous studies, and removes a long-standing discrepancy between the radius and effective temperature. A spectral disentangling technique is applied to the échelle observations and the spectra of the individual components are separated. Atmospheric and abundance analyses are performed for the mass-gaining component and we found C/N =1.55 ± 0.40 for this star. An extensive set of evolutionary models (3.5 × 106) for both components are calculated from which the best-fitting model is derived. It is found that β, the parameter which quantifies the efficiency of mass-loss from a binary system, is close to zero. This means that the mass-transfer in δ Lib is mostly conservative with little mass loss from the system

The first study of 54 new eccentric eclipsing binaries in our Galaxy

We present an analysis of the apsidal motion and light curve parameters of 54 galactic Algol-type binaries never before studied. This is the first analysis of such a large sample of eccentric eclipsing binaries in our Galaxy, and has enabled us to identify several systems that are worthy of further study. Bringing together data from various databases and surveys, supplemented with new observations, we have been able to trace the long-term evolution of the eccentric orbit over durations extending back up to several decades. Our present study explores a rather different sample of stars to those presented in the previously published catalogue of eccentric eclipsing binaries by Bulut & Demircan (2007), sampling to fainter magnitudes, covering later spectral types, sensitive to different orbital periods with more than 50% of our systems having periods longer than 6 days. The typical apsidal motion in the sample is rather slow (mostly of order of centuries long), although in some cases this is less than 50 years. All of the systems, except one, have eccentricities less than 0.5, with an average value of 0.23. Several of the stars also show evidence for additional period variability. In particular we can identify three systems in the sample, HD 44093, V611 Pup, and HD 313631, which likely represent relativistic apsidal rotators

Temporal resolution of a pre-maximum halt in a Classical Nova: V5589 Sgr observed with STEREO HI-1B

Classical novae show a rapid rise in optical brightness over a few hours. Until recently the rise phase, particularly the phenomenon of a pre-maximum halt, was observed sporadically. Solar observation satellites observing Coronal Mass Ejections enable us to observe the pre-maximum phase in un- precedented temporal resolution. We present observations of V5589 Sgr with STEREO HI-1B at a cadence of 40 min, the highest to date. We temporally resolve a pre-maximum halt for the first time, with two examples each rising over 40 min then declining within 80 min. Comparison with a grid of outburst models suggests this double peak, and the overall rise timescale, are consistent with a white dwarf mass, central temperature and accretion rate close to 1.0 M⊙, 5 × 107 K and 10−10 M⊙ yr−1 respectively. The modelling formally predicts mass loss onset at JD 2456038.2391±0.0139, 12 hrs before optical maximum. The model assumes a main–sequence donor. Observational evidence is for a subgiant companion; meaning the accretion rate is under–estimated. Post–maximum we see erratic variations commonly associated with much slower novae. Estimating the decline rate difficult, but we place the time to decline two magnitudes as 2.1 < t2(days) < 3.9 making V5589 Sgr a “very fast” nova. The brightest point defines “day 0” as JD 2456038.8224±0.0139, although at this high cadence the meaning of the observed maximum becomes difficult to define. We suggest that such erratic variability normally goes undetected in faster novae due to the low cadence of typical observations; implying erratic behaviour is not necessarily related to the rate of decline

Transition region blinkers

Blinkers are small intensity enhancements seen in the transition region of the solar atmosphere. They are important because they give us a unique insight into the transition region which until recently, has not been studied in much detail. An automated method of identifying blinkers is presented and used to identify blinkers in the quiet Sun and active regions from SOHO/CDS O V data. The general properties of the blinkers are discussed. They have typical areas of 3 x 10⁷ km² and lifetimes of 16 minutes. Their typical global frequency and intensity enhancement factors in the quiet Sun are 7s ⁻¹ and 1.8, respectively, whereas these values increase in active regions to 13s⁻¹and 2.4. Blinkers are best seen in the O V (629Å) transition-region line, but they also have strong signatures in O IV (554Å), and the chromospheric line, He I (584Å). The strongest O V blinkers can also be identified in O III (599Å). No significant signatures are found in the coronal lines Mg IX (368 Å) and Mg X (624 Å) for quiet Sun blinkers, but some increases can be seen in active-region blinkers. The ratios of the oxygen lines in blinkers were found to be flat confirming the result that blinkers are not temperature events, but are either density enhancements or increases in filling factor. Blinkers appear to occur preferentially over regions of enhanced chromospheric, transition region or coronal emission such as network boundaries. The plasma velocities of the O V blinkers and the chromosphere below have been studied. The Doppler and non-thermal velocities found are preferentially more red-shifted and greater than the normal chromospheric and transition region plasma, respectively. The ranges of these enhanced velocities, however, are no larger than the typical spread of Doppler and non-thermal velocities in these regions. Analysis of the magnetic field below blinkers shows that blinkers preferentially occur above regions of large or strong magnetic fragments with 55% of quiet Sun and 50% of active-region blinkers occurring in regions where one polarity dominates. Active-region blinkers are found above both active-region (plage) magnetic fields, as well as above the umbra and penumbra of sunspots. There appears to be no correlation between the strength of these single polarity magnetic fields or the ratio of mixed magnetic fields beneath blinkers and blinker characteristics. Furthermore, following a comparison of explosive events and blinkers, only one case is found where the two phenomena are coincident. Initial probability analysis suggests that the hypothesis that explosive events occur independently of blinkers cannot be ruled out

Imaging of a Circumsolar Dust Ring near the Orbit of Venus

The gravitational interaction of dust in the zodiacal cloud with individual planets is expected to give rise to ringlike features: Such a circumsolar ring has been observed associated with Earth, but such resonance rings have not been confirmed to exist for other planets. Here, we report on sensitive photometric observations, based on imaging from the STEREO mission, that confirm the existence of a dust ring at the orbit of Venus. The maximum overdensity of dust in this ring, compared to the zodiacal cloud, is ~10%. The radial density profile of this ring differs from the model used to describe Earth’s ring in that it has two distinct steplike components, with one step being interior and the other exterior to the orbit of Venus