A search for soft X-ray emission from stellar sources

With the soft X-ray detector (0.2–0.284 keV) aboard the Astronomical Netherlands Satellite (ANS) we have searched for X-ray emission from hot star coronae and peculiar stars. On Sirius ( CMa) and Capella ( Aur) X-ray emission has been measured at 6 and 5 level, respectively, above background. In all other cases the search revealed no evidence for soft X-ray emission. Upper limits to the luminosities of about 25 star coronae (main-sequence stars, (sub)giants, and supergiants) and of 4 peculiar stars ( Sco, Lyr, P Cyg, and Car) have been obtained.Paper presented at the COSPAR/IAU Symposium on Fast Transients in X-and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

The cascading of cosmic-ray nuclei in various media

More than a thousand interactions of primary heavy nuclei of the cosmic radiation with charge ≥10 and energy >1 GeV nucleon^?1 in nuclear emulsion have been studied with emphasis on how the primary nucleus fragments. It has been determined that the cases of multiple successive fragmentations that have been observed do not occur more frequently than expected. The fragmentation ofZ>20 nuclei does depend on the target nucleus to some extent so it is important to try to separate the interactions in emulsion by theirN _h (number of evaporation prongs). The fragmentation of ₈ ¹⁶ O at 2.1 GeV nucleon^?1 measured at the Bevalac shows a similar dependence on target nucleus. By using data from these new interactions combined with published data we have simulated on a computer nuclear cascades in both emulsion and air. Results on these cascades are given for both primary silicon and primary iron nuclei. These results are used to discuss the fluctuations expected in extensive air showers produced by heavy primary nuclei.     

On the secular variations of Io and Titan

A long-term variation of the magnitude at mean opposition is shown to exist for Io and Titan. The variation of Io seems to be correlated with the orbital period of Jupiter, the maximum light occurring at perihelion.     

Evidence for downflow following a coronal transient?

On 11 September 1973 a peculiar prominence was observed. The prominence displayed strong ( 50km s^–1) systematic motions toward and away from the observer. The unusual spectrographic appearance of the prominence might have been due to downflowing material lifted into the corona during an earlier coronal transient.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

A distinctive type of ascending prominence — ‘fountain’

Cinematographic observations of solar prominences made at Mauna Loa during the past couple of years suggest that there is a well-defined sub-class of ascending prominences characterized by closed-system transference of chromospheric material along an arch or loop (up one leg and down the other); meanwhile the entire prominence envelope steadily rises upward and expands through the corona. We denote these prominences as fountains. Several examples are described. Fountains appear to be well contained by coronal magnetic fields. Their total kinetic energy is in the order of 10³⁰ erg but dissipation is typically quite slow (over time periods like 100 min) so that the correlative disturbances (radio bursts, coronal transients, chromopsheric brightenings, etc.) are generally unspectacular or non-existent.This research was started when E. T.-H. was still on the staff of the High Altitude Observatory.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Geopotential harmonics of order 15 and even degree,from changes in orbital eccentricity at resonance

When a satellite orbit decaying slowly under the action of air drag experiences 15th-order resonance with the Earth's gravitational field, so that the ground track repeats after 15 rev, the orbital eccentricity may suffer appreciable changes due to perturbations from the gravitational harmonics of order 15 and even degree (16, 18, 20…). In this paper the changes in eccentricity at resonance for six satellites in near-circular orbits at inclinations between 56 and 90° have been analysed to derive 11 pairs of equations linking the harmonic coefficients of order 15 and (even) degree l, $\text{C}{}_{\mathrm{l,15}}\text{and}\text{S}{}_{\mathrm{l,15}}$ in the usual notation. These equations (together with eight constraint equations) are solved to give:

     

958.

Geopotential harmonics of order 15 and odd degree from analysis of resonant orbits     

D.G. King-Hele  Doreen M.C. Walker  R.H. Gooding 《Planetary and Space Science》1975,23(9):1239-1256

We have analysed the variations of inclination in 13 satellite orbits as they pass slowly, under the action of air drag, through 15th-order resonance with the geopotential, when successive equatorial crossings are 24° apart and the ground track repeats after 15 rev. The size and form of the change in inclination are determined mainly by the values of the geopotential harmonics of 15th order and odd degree, $\text{C}\text{?}{}_{\mathrm{l,15}}$ and $\text{S}\text{?}{}_{\mathrm{l,15}}$ (with l = 15, 17, 19, …) in the usual notation. Our analysis gives values of these coefficients up to l = 33 as follows:

$\text{l}$	109$\text{C}{}_{\mathrm{l,15}}$	109$\text{S}{}_{\mathrm{l,15}}$
16	?13.7 ± 1.3	?18.5 ± 2.7
18	?42.3 ± 1.8	?34.7 ± 3.4
20	10.5 ± 3.1	29.8 ± 5.2
22	?8.6 ± 3.8	?20.2 ± 7.4

     

959.

Coronal changes associated with a disappearing filament     

N. R. Sheeley Jr.  J. D. Bohlin  G. E. Brueckner  J. D. Purcell  V. E. Scherrer  R. Tousey  J. B. Smith Jr.  D. M. Speich  E. Tandberg-Hanssen  R. M. Wilson  A. C. De Loach  R. B. Hoover  J. P. Mc Guire 《Solar physics》1975,45(2):377-392

This paper describes Skylab/ATM observations of the events associated with a disappearing filament near the center of the solar disk on January 18, 1974. As the filament disappeared, the nearby coronal plasma was heated to a temperature in excess of 6 × 10⁶K. A change in the pattern of coronal emission occurred during the 11/3 hr period that the soft X-ray flux was increasing. This change seemed to consist of the formation and apparent expansion of a loop-like coronal structure which remained visible until its passage around the west limb several days later. The time history of the X-ray and microwave radio flux displayed the well-known gradual-rise-and-fall (GRF) signature, suggesting that this January 18 event may have properties characteristic of a wide class of X-ray and radio events.In pursuit of this idea, we examined other spatially-resolved Skylab/ATM observations of long-duration X-ray events to see what characteristics they may have in common. Nineteen similar long-lived SOLRAD X-ray events having either the GRF or post-burst radio classification occurred during the nine-month Skylab mission. Sixteen of these occurred during HAO/ATM coronagraph observations, and 7 of these 16 events occurred during observations with both the NRL/ATM slitless spectrograph and the MSFC-A/ATM X-ray telescope. The tabulation of these events suggests that all long-lived SOLRAD X-ray bursts involve transients in the outer corona and that at least two-thirds of the bursts involve either the eruption or major activation of a prominence. Also, these observations indicate that long-lived SOLARD events are characterized by the appearance of new loops of emission in the lower corona during the declining phase of the X-ray emission. However, sometimes these loops disappear after the X-ray event (like the post-flare loops associated with a sporadic coronal condensation), and sometimes the loops remain indefinitely (like the emission from a permanent coronal condensation).Visiting Scientist, Kitt Peak National Observatory, Tucson, Ariz. 85726, U.S.A. operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.Presently located at NASA/MSFC, Space Sciences Laboratory, Marshall Space Flight Center, Ala. 35812, U. S.A.     

960.

Relationship of intertidal surface sediment chlorophyll concentration to hyperspectral reflectance and chlorophyll fluorescence     

Jacco C. Kromkamp  Edward P. Morris  Rodney M. Forster  Claire Honeywill  Scott Hagerthey  David M. Paterson 《Estuaries and Coasts》2006,29(2):183-196

Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence, especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics. At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation, F_o ¹⁵), sediment water content, and chlorophylla concentrations were taken (including breakdown products: [chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes; we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation index (NDVI) was found to be most strongly correlated to sediment [chla+phaeo], except for the predominantly sandy Sylt stations. F_o ¹⁵ was also significantly correlated to sediment [chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between NDVI or fluorescence and [chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially for F_o ¹⁵. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment analysis. NDVI appears to be a robust proxy for sediment [chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries.     

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l	109C?l,15	109S?l,15
15	?23.5 ± 0.8	?7.7 ± 0.8
17	6.3 ± 1.5	5.6 ± 1.5
19	?25.1 ± 2.5	?7.3 ± 2.3
21	27.8 ± 3.6	?0.7 ± 3.4
23	17.1 ± 4.1	13.9 ± 4.8
25	?1.1 ± 3.0	8.5 ± 4.2
27	10.0 ± 3.3	6.7 ± 2.7
29	?9.4 ± 3.5	0.1 ± 4.7
31	10.1 ± 5.4	3.8 ± 5.6
33	1.1 ± 5.7	3.1 ± 5.8

Geopotential harmonics of order 15 and odd degree from analysis of resonant orbits

We have analysed the variations of inclination in 13 satellite orbits as they pass slowly, under the action of air drag, through 15th-order resonance with the geopotential, when successive equatorial crossings are 24° apart and the ground track repeats after 15 rev. The size and form of the change in inclination are determined mainly by the values of the geopotential harmonics of 15th order and odd degree, $\text{C}\text{?}{}_{\mathrm{l,15}}$ and $\text{S}\text{?}{}_{\mathrm{l,15}}$ (with l = 15, 17, 19, …) in the usual notation. Our analysis gives values of these coefficients up to l = 33 as follows:

Coronal changes associated with a disappearing filament

This paper describes Skylab/ATM observations of the events associated with a disappearing filament near the center of the solar disk on January 18, 1974. As the filament disappeared, the nearby coronal plasma was heated to a temperature in excess of 6 × 10⁶K. A change in the pattern of coronal emission occurred during the 11/3 hr period that the soft X-ray flux was increasing. This change seemed to consist of the formation and apparent expansion of a loop-like coronal structure which remained visible until its passage around the west limb several days later. The time history of the X-ray and microwave radio flux displayed the well-known gradual-rise-and-fall (GRF) signature, suggesting that this January 18 event may have properties characteristic of a wide class of X-ray and radio events.In pursuit of this idea, we examined other spatially-resolved Skylab/ATM observations of long-duration X-ray events to see what characteristics they may have in common. Nineteen similar long-lived SOLRAD X-ray events having either the GRF or post-burst radio classification occurred during the nine-month Skylab mission. Sixteen of these occurred during HAO/ATM coronagraph observations, and 7 of these 16 events occurred during observations with both the NRL/ATM slitless spectrograph and the MSFC-A/ATM X-ray telescope. The tabulation of these events suggests that all long-lived SOLRAD X-ray bursts involve transients in the outer corona and that at least two-thirds of the bursts involve either the eruption or major activation of a prominence. Also, these observations indicate that long-lived SOLARD events are characterized by the appearance of new loops of emission in the lower corona during the declining phase of the X-ray emission. However, sometimes these loops disappear after the X-ray event (like the post-flare loops associated with a sporadic coronal condensation), and sometimes the loops remain indefinitely (like the emission from a permanent coronal condensation).Visiting Scientist, Kitt Peak National Observatory, Tucson, Ariz. 85726, U.S.A. operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.Presently located at NASA/MSFC, Space Sciences Laboratory, Marshall Space Flight Center, Ala. 35812, U. S.A.     

Relationship of intertidal surface sediment chlorophyll concentration to hyperspectral reflectance and chlorophyll fluorescence

Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence, especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics. At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation, F_o ¹⁵), sediment water content, and chlorophylla concentrations were taken (including breakdown products: [chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes; we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation index (NDVI) was found to be most strongly correlated to sediment [chla+phaeo], except for the predominantly sandy Sylt stations. F_o ¹⁵ was also significantly correlated to sediment [chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between NDVI or fluorescence and [chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially for F_o ¹⁵. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment analysis. NDVI appears to be a robust proxy for sediment [chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries.