119307857
Determination of the Topology Skeleton of Magnetic Fields in a Solar Active Region
Magnetic topology has been a key to the understanding of magnetic energy release mechanism. Based on observed vector magnetograms, we have determined the three-dimensional (3D) topology skeleton of the magnetic fields in the active region NOAA 10720. The skeleton consists of six 3D magnetic nulls and a network of corresponding spines, fans, and null-null lines. For the first time, we have identified a spiral magnetic null in Sun's corona. The magnetic lines of force twisted around the spine of the null, forming a `magnetic wreath' with excess of free magnetic energy and resembling observed brightening structures at extra-ultraviolet (EUV) wavebands. We found clear evidence of topology eruptions which are referred to as catastrophic changes of topology skeleton associated with a coronal mass ejection (CME) and an explosive X-ray flare. These results shed new lights on the structural complexity and its role in explosive magnetic activity. The concept of flux rope has been widely used in modelling explosive magnetic activity, although their observational identity is rather obscure or, at least, lacking of necessary details up to date. We suggest that the magnetic wreath associated with the 3D spiral null is likely an important class of the physical entity of flux ropes.
15057212
Mode selection mechanism and magnetic diffusivity in a non-axisymmetric solar dynamo model
The generation of solar non-axisymmetric magnetic fields is studied based on a linear � 2 − dynamo model in a rotating spherical frame. The model consists of a solarlike differential rotation, a magnetic diffusivity varied with depth, and three types of �-effects with different locations, i.e. the tachocline, the whole convective zone and the sub-surface. Some comparisons of the critical �-values of axisymmetric (m = 0) and longitude-dependent modes (m = 1,2,3) are presented to show the roles of the magnetic diffusivity in the problem of modes selection. With the changing of diffusivity intensity for the given solar differential rotation system, the dominant mode possibly changes likewise and the stronger the diffusivity is, the easier the non-axisymmetric modes are excited. The influence of the diffusivity and differential rotation on the configurations of the dominant modes are also presented.
16400877
VECTOR MAGNETIC FIELDS OF SOLAR GRANULATION
Observations of the quiet Sun from the Solar Optical Telescope/Spectro-Polarimeter aboard the Hinode spacecraft reveal the magnetic characteristics of the solar photosphere. By making use of the deep-mode observations of three quiet regions, we have statistically studied the vector magnetic fields of solar granulation. More than 2000 normal granules are manually selected to form a sample. It is recognized that some granules are even darker than the mean photosphere in intensity, and there is a linear correlation between intensity and Doppler velocity in the granules. The distributions of longitudinal and transverse apparent magnetic flux densities, Doppler velocity, and continuum intensity of granules are obtained, and their unsigned magnetic flux measured. Two approaches are used in this study. First, we obtained the magnetic properties of granulation by averaging the measurements for all the sampling granules. Second, we reconstructed an average granular cell based on a subsample, and obtained the detailed distribution of apparent magnetic flux density within the model granular cell. All the results have been compared with those for intergranular lanes and a few typical abnormal granules. Our statistical analysis reveals the following results. (1) The unsigned magnetic flux of individual granules spans the range from 1.1 × 1015 Mx to 3.3 × 1018 Mx with a peak distribution at 1.6 × 1016 Mx. (2) The unsigned longitudinal apparent flux density of granules ranges from almost 0 to 212 Mx cm–2 with a mean longitudinal apparent flux density of 12 Mx cm–2, while the transverse apparent flux density of granules ranges from 4 to 218 Mx cm–2 with a mean transverse apparent flux density of 79 Mx cm–2. The longitudinal and transverse apparent magnetic flux densities of granules are positively correlated, and the longitudinal apparent flux density of granules is weaker than the corresponding transverse apparent flux density. (3) The magnetic inclination of granules with respect to the surface that is perpendicular to the line of sight falls in the range of 4.8-76.7 degrees with a peak distribution at 25 degrees. On average, the magnetic vectors in granules are more vertical than those in the intergranular lanes. (4) There is a strong preference that both the vertical and horizontal fields on the quiet Sun reside in the intergranular lanes. (5) The detailed distributions of apparent flux density, Doppler velocity, and continuum intensity within an average granular cell are presented. These distributions can be empirically formulated well.
59126004
The velocity structure of moving magnetic feature pairs around sunspots: support for the U-loop model
Context. Moving magnetic feature (MMF) pairs are among the most significant fine-scale structures around sunspots. Several models have been proposed to interpret the origin and evolution of MMF pairs. These models provide important clues to understanding MMF pairs. Aims. We present an analysis of the velocity structure of MMF pairs in order to put further constrains on the MMF models. Methods. Using continuum images, longitudinal magnetograms and Dopplergrams, recorded by the Michelson Doppler Imager (MDI) instrument on the Solar and Heliospheric Observatory (SOHO), we have traced 123 pairs of opposite magnetic polarity moving magnetic features (MMFs) in three active regions NOAA ARs 8375, 0330 and 9575. At the time of observation, AR 8375 was young, AR 0330 mature, and AR 9575 decaying. Results. The vertical velocity, measured from MDI Dopplergrams for the three active regions, indicates that the elements of MMF pairs with polarity opposite to that of the sunspot support a downflow (Doppler redshift) of around 50-100 m s -1 . The average Doppler shift difference between negative and positive elements of an MMF pair is about 150 m s -1 in AR 8375, 100 m s -1 in AR 0330, and 20 m s -1 in AR 9575. These observational results are in agreement with the model where MMF pairs are part of a U-loop emanating from the sunspot's magnetic canopy. According to this model, the downflow is caused by the Evershed flow returning below the solar surface. For AR 8375, the horizontal velocity of MMFs ranges from 0.1 km s -1 to 0.7 km s -1 , and on average, the velocity of an MMF pair decreases significantly (from 0.6 km s -1 to 0.35 km s -1 ) with increasing distance from the MMF's birth place. In contrast, the decrease of the average velocity is far less obvious from 0.5 km s -1 to 0.4 km s -1 with increasing distance from the sunspot. This result suggests that the change in MMF flow speed does not reflect the radial structure of the moat flow, but rather is intrinsic to the evolution of the MMF pairs. This result is also in agreement with the U-loop model of MMF pairs. We also find that properties of MMF pairs, most strikingly the lifetime, depend on the evolution stages of the parent sunspot. The mean lifetimes of MMF pairs in ARs 9575 and 0330 are 0.7 h and 1.6 h, respectively, which is considerably shorter than the 4 h lifetime previously found for AR 8375.
119129472
Magnetic Evolution and Temperature Variation in a Coronal Hole
We have explored the magnetic flux evolution and temperature variation in a coronal hole region, using Big Bear Solar Observatory deep magnetograms and SOHO EIT images observed from 2005 October 10 to 14. For comparison, we also investigated a neighboring quiet region of the Sun. The coronal hole evolved from its mature stage to its disappearance during the observing period. We have obtained the following results: (1) When the coronal hole was well developed on October 10, about 60% of the magnetic flux was positive. The EUV brightness was 420 counts pixel-1, and the coronal temperature, estimated from the line ratio of the EIT 195 and 171 A images, was 1.07 MK. (2) On October 14, when the coronal hole had almost disappeared, 51% of the magnetic flux was positive, the EUV radiance was 530 counts pixel-1, and the temperature was 1.10 MK. (3) In the neighboring quiet region, the fraction of positive flux varied between 0.49 and 0.47. The EUV brightness displayed an irregular variation, with a mean value of 870 counts pixel-1. The temperature was almost constant at 1.11 MK during the 5 day observation. Our results demonstrate that in a coronal hole less imbalance of the magnetic flux in opposite polarities leads to stronger EUV brightness and higher coronal temperatures.
14786946
The Properties of Horizontal Magnetic Elements in Quiet Solar Intranetwork
Using the data observed by the Solar Optical Telescope/Spectropolarimeter aboard the Hinode satellite, the horizontal and vertical fields are derived from the wavelength-integrated measures of Zeeman-induced linear and circular polarizations. The quiet intranetwork regions are pervaded by horizontal magnetic elements. We categorize the horizontal intranetwork magnetic elements into two types: one is the nonisolated element which is accompanied by the vertical magnetic elements during its evolution; another is the isolated element which is not accompanied by the vertical magnetic elements. Their properties, such as lifetime, size, and magnetic flux density, are studied, and the relationships among various magnetic parameters are investigated. We identify 446 horizontal intranetwork magnetic elements among them 87 elements are isolated and 359 are nonisolated. Quantitative measurements reveal that the isolated elements have relatively weaker horizontal magnetic fields, almost equal size, and shorter lifetime compared with the nonisolated elements. Most nonisolated horizontal intranetwork magnetic elements are identified to associate with the emergence of {omega}-shaped flux loops. A few nonisolated elements seem to indicate scenarios of submergence of {omega} loops or emergence of U-like loops. There is a positive correlation between the lifetime and the size for both the isolated and nonisolated horizontal intranetwork field elements (HIFs). Positivemore » correlation between the lifetime and the magnetic flux density for nonisolated HIFs is also found, but no correlation for isolated HIFs. Even though the horizontal elements show lower magnetic flux density, they could carry the total magnetic flux in the order of magnitude close to 10{sup 25} Mx to the solar surface each day.« less
44247007
VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. II. A SHORT-PERIOD COMPANION ORBITING AN F STAR WITH EVIDENCE OF A STELLAR TERTIARY AND SIGNIFICANT MUTUAL INCLINATION
We report the discovery via radial velocity (RV) measurements of a short-period (P = 2.430420 ± 0.000006 days) companion to the F-type main-sequence star TYC 2930-00872-1. A long-term trend in the RV data also suggests the presence of a tertiary stellar companion with P > 2000 days. High-resolution spectroscopy of the host star yields T_(eff) = 6427 ± 33 K, log g = 4.52 ± 0.14, and [Fe/H] = –0.04 ± 0.05. These parameters, combined with the broadband spectral energy distribution (SED) and a parallax, allow us to infer a mass and radius of the host star of M_1 = 1.21 ± 0.08 M_☉ and R_1 = 1.09^(+0.15)_(–0.13) R_☉. The minimum mass of the inner companion is below the hydrogen-burning limit; however, the true mass is likely to be substantially higher. We are able to exclude transits of the inner companion with high confidence. Further, the host star spectrum exhibits a clear signature of Ca H and K core emission, indicating stellar activity, but a lack of photometric variability and small v sin I suggest that the primary's spin axis is oriented in a pole-on configuration. The rotational period of the primary estimated through an activity-rotation relation matches the orbital period of the inner companion to within 1.5 σ, suggesting that the primary and inner companion are tidally locked. If the inner companion's orbital angular momentum vector is aligned with the stellar spin axis as expected through tidal evolution, then it has a stellar mass of ~0.3-0.4 M_☉. Direct imaging limits the existence of stellar companions to projected separations <30 AU. No set of spectral lines and no significant flux contribution to the SED from either companion are detected, which places individual upper mass limits of M_([2,3]) ≾ 1.0 M_☉, provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of ~0.5-0.6 M_☉, and its orbit is likely significantly inclined from that of the secondary, suggesting that the Kozai-Lidov mechanism may have driven the dynamical evolution of this system.
59132262
Quantifying solar superactive regions with vector magnetic field observations
Context. The vector magnetic field characteristics of superactive regions (SARs) hold the key for understanding why SARs are extremely active and provide the guidance in space weather prediction. Aims. We aim to quantify the characteristics of SARs using the vector magnetograms taken by the Solar Magnetic Field Telescope at Huairou Solar Observatory Station. Methods. The vector magnetic field characteristics of 14 SARs in solar cycles 22 and 23 were analyzed using the following four parameters: 1) the magnetic flux imbalance between opposite polarities; 2) the total photospheric free magnetic energy; 3) the length of the magnetic neutral line with its steep horizontal magnetic gradient; and 4) the area with strong magnetic shear. Furthermore, we selected another eight large and inactive active regions (ARs), which are called fallow ARs (FARs), to compare them with the SARs. Results. We found that most of the SARs have a net magnetic flux higher than 7.0×10 21 Mx, a total photospheric free magnetic energy higher than 1.0 ×10 24 ergcm −1 , a magnetic neutral line with a steep horizontal magnetic gradient (≥300 GMm −1 ) longer than 30 Mm, and an area with strong magnetic shear (shear angle ≥80 ◦ ) greater than 100 Mm 2 . In contrast, the values of these parameters for the FARs are mostly very low. The Pearson χ 2 test was used to examine the significance of the difference between the SARs and FARs, and the results indicate that these two types of ARs can be fairly distinguished by each of these parameters. The significance levels are 99.55%, 99.98%, 99.98%, and 99.96%, respectively. However, no single parameter can distinguish them perfectly. Therefore we propose a composite index based on these parameters, and find that the distinction between the two types of ARs is also significant with a significance level of 99.96%. These results are useful for a better physical understanding of the SAR and FAR.
118446261
ON THE X-RAY BALDWIN EFFECT IN ACTIVE GALACTIC NUCLEI OBSERVED BY THE CHANDRA HIGH-ENERGY GRATING
Using Chandra high-energy grating (HEG) observations of 32 active galactic nuclei (AGNs), we present a systematic study of the X-ray Baldwin effect (XBE; i.e., the anti-correlation between the narrow Fe Kα line equivalent width (EW) and X-ray continuum luminosity for AGN samples) with the highest spectral resolution currently available. We have previously reported an anti-correlation with EW∝L –0.22 2-10 keV in an HEG sample, and the correlation is much weaker after averaging multiple observations of individual AGNs (EW∝L –0.13 2-10 keV). This indicates that rapid variation in the X-ray continuum plays an important role in producing the XBE, and such an effect should also be visible in individual AGNs. In this Letter, by normalizing the line EWs and continuum luminosities to the time-averaged values for each AGN in our sample with multiple HEG observations, we find a strong anti-correlation between EW and LX (EW/EW∝(L/L)–0.82 ± 0.10), consistent with the XBE expected in an individual AGN if the narrow line flux remains constant while the continuum varies. This is first observational evidence that the Fe Kα line flux in a large sample of AGNs lacks a corresponding response to the continuum variation, supporting the fact that the narrow Fe-K line emission originates from a region far from the nucleus. We then performed Monte Carlo simulations to address whether the global XBE can be produced by X-ray continuum variation solely, and found that such an interpretation of the XBE cannot be ruled out statistically. One should thus be very cautious before drawing any scientific conclusion based on an observed XBE.
209834941
Search for heavy long-lived charged particles in $pp$ collisions at $s=7$ TeV
The result of a search for heavy long-lived charged particles produced in pp collisions at sqrt(s) = 7 TeV at the LHC is described. The data sample has been collected using the CMS detector and corresponds to an integrated luminosity of 5.0 inverse femtobarns. The inner tracking detectors are used to define a sample of events containing tracks with high momentum and high ionization energy loss. A second sample of events with high-momentum and high-ionization tracks satisfying muon identification and long time-of-flight criteria is analyzed independently. In both cases, the results are consistent with the expected background estimated from data. The results are used to establish cross section limits as a function of mass within the context of models with long-lived gluinos, scalar top quarks and scalar taus. Cross section limits on hyper-meson particles, containing new elementary long-lived hyper-quarks predicted by a vector-like confinement model, are also presented. Lower limits at 95% confidence level on the mass of gluinos (scalar top quarks) are found to be 1098 (737) GeV. A limit of 928 (626) GeV is set for a gluino (scalar top quark) that hadronizes into a neutral bound state before reaching the muon detectors. The lower mass limit for a pair produced scalar tau is found to be 223 GeV. Mass limits for a hyper-kaon are placed at 484, 602, and 747 GeV for hyper-rho masses of 800, 1200, and 1600 GeV, respectively.
115754528
GEM technical design report