A Study of the Extragalactic UV Radiation in Helix Nebula using GALEX

We have studied the ultraviolet sources using Galaxy Evolution Explorer medium imaging surveys in Helix Nebula and estimated UV fluxes by using aperture photometry in distant and near ultraviolet bands. The aperture photometric method produces reliable, accurate flux measurements and found inconsistent with the merged catalog of Galaxy Evolution Explorer. From the current results, the fluxes are consistent with brighter absolute magnitude up to 24.5 and the measurement error increases gradually to more than 50 % at the fainter magnitude side. Percentage of error in far UV is greater than near UV, due to the fact that brighter galaxies are more visible than the near UV sources. The diffuse UV contributors of zodiacal light, airglow contribution in the nebula were estimated. The total extragalactic UV radiation from the detected sources to the diffuse background in the nebula is of the order of 50 ± 14 photons cm-2sr-1s-1Å-1 in NUV band and 28 ±10 photons cm-2sr-1s-1Å-1 in FUV band. HIGHLIGHTS GALEX observations have the potential to find extragalactic UV sources Helix Nebula is first identified for distinct source detection Aperture photometric method can detect fainter sources up to the magnitude of 27 Extragalactic sources in the Helix nebula contribute to diffuse UV emission in the nebula GRAPHICAL ABSTRACT

Comet fragmentation as a source of the zodiacal cloud

<p>Models of the thermal emission of the zodiacal cloud and sporadic meteoroids suggest that the dominant source of interplanetary dust is Jupiter-family comets (JFCs). However, comet sublimation is insufficient to sustain the quantity of dust presently in the inner solar system. It has therefore been suggested that spontaneous disruptions of JFCs may supply the zodiacal cloud.</p> <p>We present a model for the dust produced in comet fragmentations and its evolution, comparing with the present day zodiacal cloud. Using results from dynamical simulations we follow individual JFCs as they evolve and undergo recurrent splitting events. The dust produced by these events is followed with a kinetic model which takes into account the effects of collisional evolution, Poynting-Robertson drag, and radiation pressure. This allows us to model both the size distribution and radial profile of dust resulting from comet fragmentation. Our model suggests that JFC fragmentations can produce enough dust to sustain the zodiacal cloud. We also discuss the feasibility of comet fragmentation producing the spatial and size distribution of dust seen in the zodiacal cloud.</p> <p>By modelling individual comets we are also able to explore the variability of cometary input to the zodiacal cloud. Comets are drawn from a size distribution based on the Kuiper belt and fragment randomly. We show that large comets should be scattered into the inner solar system stochastically, leading to large variations in the historical brightness of the zodiacal light.</p>

The Space Dust That Causes Zodiacal Light Might Come from Mars

Serendipitous observations by the Juno spacecraft while it was en route to Jupiter suggest a Martian source for the dust, but how the dust escapes Mars or its moons remains unknown.

The influence of the dust-free zone on F-corona brightness

<p>This presentation is related to model calculations of the circumsolar dust brightness that is seen in the F-corona and inner Zodiacal light. We calculate the brightness integral that includes the size distribution of the interplanetary dust, the spatial distribution, and the scattering properties. The scattering properties are estimated with Mie calculations of spherical particles consisting of astronomical silicate. We consider different size distributions of the dust particles with sizes between 1 nanometre - 100 micrometre. It was recently discussed that the extension of the dust-free zone can be inferred from the slope of the F-corona brightness seen in new observations received from the WISPR instrument on the NASA Parker Solar Probe (Stenborg et al., 2020). We, therefore, investigate the influence of the dust-free zone on the brightness and compare it to the influence that the dust size distribution has.</p><p>References</p><p>1. G. Stenborg, R. A. Howard, P. Hess, B. Gallagher, PSP/WISPR observations of dust density depletion near the Sun I. Remote observations to 8 Rsol from an observer between 0.13-0.35 AU, A&A, Forthcoming article, 2020. DOI: 10.1051/0004-6361/202039284</p>

Impact induced electric field signals observed by the Solar Orbiter/RPW

<p>A large-amplitude impact-induced like electric field signal is often observed by the Radio and Plasma Wave (RPW) Instrument onboard Solar Orbiter. The signal has a sharp increase followed by an exponential decay, typically observed when spacecraft experiences a dust impact. The amplitude can reach several V/m. The impact dust size can be estimated from the electric field amplitude and is similar to the characteristic dust size near the sun expected from the zodiacal-light observations. On the other hand, the signal's decay time is the order of second, unusually long compared to the dust impact signals previously reported by the other spacecraft. We will show the characteristics of these signals and discuss the origin.</p>

A multi-band map of the natural night sky brightness including Gaia and Hipparcos integrated starlight

The natural night sky brightness is a relevant input for monitoring the light pollution evolution at observatory sites, by subtracting it from the overall sky brightness determined by direct measurements. It is also instrumental for assessing the expected darkness of the pristine night skies. The natural brightness of the night sky is determined by the sum of the spectral radiances coming from astrophysical sources, including zodiacal light, and the atmospheric airglow. The resulting radiance is modified by absorption and scattering before it reaches the observer. Therefore, the natural night sky brightness is a function of the location, time and atmospheric conditions. We present in this work GAMBONS (GAia Map of the Brightness Of the Natural Sky), a model to map the natural night brightness of the sky in cloudless and moonless nights. Unlike previous maps, GAMBONS is based on the extra-atmospheric star radiance obtained from the Gaia catalogue. The Gaia-DR2 archive compiles astrometric and photometric information for more than 1.6 billion stars up to G =21 magnitude. For the brightest stars, not included in Gaia-DR2, we have used the Hipparcos catalogue instead. After adding up to the star radiance the contributions of the diffuse galactic and extragalactic light, zodiacal light and airglow, and taking into account the effects of atmospheric attenuation and scattering, the radiance detected by ground-based observers can be estimated. This methodology can be applied to any photometric band, if appropriate transformations from the Gaia bands are available. In particular, we present the expected sky brightness for V(Johnson), and visual photopic and scotopic passbands.