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Pereira T.M.D.,NASA | Pereira T.M.D.,Lockheed Martin | De Pontieu B.,Lockheed Martin | Carlsson M.,Institute of Theoretical Astrophysics | Carlsson M.,University of Oslo
Astrophysical Journal | Year: 2012

Understanding the dynamic solar chromosphere is fundamental in solar physics. Spicules are an important feature of the chromosphere, connecting the photosphere to the corona, potentially mediating the transfer of energy and mass. The aim of this work is to study the properties of spicules over different regions of the Sun. Our goal is to investigate if there is more than one type of spicule, and how spicules behave in the quiet Sun, coronal holes, and active regions. We make use of high cadence and high spatial resolution Ca II H observations taken by Hinode/Solar Optical Telescope. Making use of a semi-automated detection algorithm, we self-consistently track and measure the properties of 519 spicules over different regions. We find clear evidence of two types of spicules. Type I spicules show a rise and fall and have typical lifetimes of 150-400 s and maximum ascending velocities of 15-40 km s -1, while typeII spicules have shorter lifetimes of 50-150 s, faster velocities of 30-110 km s-1, and are not seen to fall down, but rather fade at around their maximum length. Type II spicules are the most common, seen in the quiet Sun and coronal holes. Type I spicules are seen mostly in active regions. There are regional differences between quiet-Sun and coronal hole spicules, likely attributable to the different field configurations. The properties of typeII spicules are consistent with published results of rapid blueshifted events (RBEs), supporting the hypothesis that RBEs are their disk counterparts. For typeI spicules we find the relations between their properties to be consistent with a magnetoacoustic shock wave driver, and with dynamic fibrils as their disk counterpart. The driver of typeII spicules remains unclear from limb observations. © 2012 The American Astronomical Society. All rights reserved. Source


Judge P.G.,High Altitude Observatory | Carlsson M.,Institute of Theoretical Astrophysics
Astrophysical Journal | Year: 2010

Broadband images in the Ca ii H line, from the Broadband Filter Imager (BFI) instrument on the Hinode spacecraft, show emission from spicules emerging from and visible right down to the observed limb. Surprisingly, little absorption of spicule light is seen along their lengths. We present formal solutions to the transfer equation for given (ad hoc) source functions, including a stratified chromosphere from which spicules emanate. The model parameters are broadly compatible with earlier studies of spicules. The visibility of Ca ii spicules down to the limb in Hinode data seems to require that spicule emission be Doppler shifted relative to the stratified atmosphere, either by supersonic turbulent or organized spicular motion. The non-spicule component of the chromosphere is almost invisible in the broadband BFI data, but we predict that it will be clearly visible in high spectral resolution data. Broadband Ca ii H limb images give the false impression that the chromosphere is dominated by spicules. Our analysis serves as a reminder that the absence of a signature can be as significant as its presence. © 2010. The American Astronomical Society. All rights reserved. Source


Pereira T.M.D.,NASA | Pereira T.M.D.,Lockheed Martin | De Pontieu B.,Lockheed Martin | Carlsson M.,Institute of Theoretical Astrophysics | Carlsson M.,University of Oslo
Astrophysical Journal | Year: 2013

Spicules have been observed on the Sun for more than a century, typically in chromospheric lines such as Hα and Ca II H. Recent work has shown that so-called "type II" spicules may have a role in providing mass to the corona and the solar wind. In chromospheric filtergrams these spicules are not seen to fall back down, and they are shorter lived and more dynamic than the spicules that have been classically reported in ground-based observations. Observations of type II spicules with Hinode show fundamentally different properties from what was previously measured. In earlier work we showed that these dynamic type II spicules are the most common type, a view that was not properly identified by early observations. The aim of this work is to investigate the effects of spatio-temporal resolution in the classical spicule measurements. Making use of Hinode data degraded to match the observing conditions of older ground-based studies, we measure the properties of spicules with a semi-automated algorithm. These results are then compared to measurements using the original Hinode data. We find that degrading the data has a significant effect on the measured properties of spicules. Most importantly, the results from the degraded data agree well with older studies (e.g., mean spicule duration more than 5 minutes, and upward apparent velocities of about 25 km s-1). These results illustrate how the combination of spicule superposition, low spatial resolution and cadence affect the measured properties of spicules, and that previous measurements can be misleading. © 2013. The American Astronomical Society. All rights reserved. Source


Donkov S.,Technical University of Sofia | Veltchev T.V.,Sofia University | Veltchev T.V.,Institute of Theoretical Astrophysics | Klessen R.S.,Institute of Theoretical Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2011

We study the mass-density relationship n∝mx in molecular cloud condensations (clumps), considering various equipartition relations between their gravitational, kinetic, internal and magnetic energies. Clumps are described statistically, with a density distribution that reflects a lognormal probability density function in turbulent cold interstellar medium. The clump mass-density exponent x derived at different scales L varies in most of the cases within the range -2.5 ≲x≲-0.2, with a pronounced scale dependence and in consistency with observations. When derived from the global size-mass relationship for set of clumps, generated at all scales, the clump mass-density exponent has typical values -3.0 ≲x(γglob) ≲-0.3 that depend on the forms of energy, included in the equipartition relations, and on the velocity scaling law, whereas the description of clump geometry is important when magnetic energy is taken into account. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Veltchev T.V.,Sofia University | Veltchev T.V.,Institute of Theoretical Astrophysics | Klessen R.S.,Institute of Theoretical Astrophysics | Clark P.C.,Institute of Theoretical Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2011

In this work, we derive the stellar initial mass function (IMF) from the superposition of mass distributions of dense cores, generated through gravoturbulent fragmentation of unstable clumps in molecular clouds (MCs) and growing through competitive accretion. MCs are formed by the turbulent cascade in the interstellar medium at scales L from 100 down to ∼0.1pc. Their internal turbulence is essentially supersonic and creates clumps with a lognormal distribution of densities n. Our model is based on the assumption of a power-law relationship between clump mass and clump density: n∝mx, where x is a scale-free parameter. Gravitationally unstable clumps are assumed to undergo isothermal fragmentation and produce protostellar cores with a lognormal mass distribution, centred around the clump Jeans mass. Masses of individual cores are then assumed to grow further through competitive accretion until the rest of the gas within the clump is being exhausted. The observed IMF is best reproduced for a choice of x= 0.25, for a characteristic star formation time-scale of ∼5Myr and for a low star formation efficiency of ∼10 per cent. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS. Source

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