72 research outputs found
Digitization of sunspot drawings by Sp\"orer made in 1861-1894
Most of our knowledge about the Sun's activity cycle arises from sunspot
observations over the last centuries since telescopes have been used for
astronomy. The German astronomer Gustav Sp\"orer observed almost daily the Sun
from 1861 until the beginning of 1894 and assembled a 33-year collection of
sunspot data covering a total of 445 solar rotation periods. These sunspot
drawings were carefully placed on an equidistant grid of heliographic longitude
and latitude for each rotation period, which were then copied to copper plates
for a lithographic reproduction of the drawings in astronomical journals. In
this article, we describe in detail the process of capturing these data as
digital images, correcting for various effects of the aging print materials,
and preparing the data for contemporary scientific analysis based on advanced
image processing techniques. With the processed data we create a butterfly
diagram aggregating sunspot areas, and we present methods to measure the size
of sunspots (umbra and penumbra) and to determine tilt angles of active
regions. A probability density function of the sunspot area is computed, which
conforms to contemporary data after rescaling.Comment: 10 pages, 8 figures, accepted for publication in Astronomische
Nachrichten/Astronomical Note
Estimating meteor rates using Bayesian inference
A method for estimating the true meteor rate lambda from a small number of observed meteors n is derived. We employ Bayesian inference with a Poissonian likelihood function. We discuss the choice of a suitable prior and propose the adoption of Jeffreys prior, P(lambda)=lambda^-0.5, which yields an expectation value E(lambda) = n+0.5 for any n >= 0. We update the ZHR meteor activity formula accordingly, and explain how 68%- and 95%-confidence intervals can be computed.Peer reviewe
First solar butterfly diagram from Schwabe's observations in 1825-1867
The original sunspot observations by Heinrich Samuel Schwabe of 1825-1867
were digitized and a first subset of spots was measured. In this initial
project, we determined more than 14 000 sunspot positions and areas comprising
about 11% of the total amount of spots available from that period. The
resulting butterfly diagram has a typical appearance, but with evident
north-south asymmetries.Comment: 3 pages, 1 figure, Proceedings of IAU symposium 273, Physics of Sun
and star spots, Ventura, California 22-26 August 201
Nonlinear dynamo models using quasi-biennial oscillations constrained by sunspot area data
Contex: Solar magnetic activity exhibits variations with periods between
1.5--4 years, the so-called quasi-biennial oscillations (QBOs), in addition to
the well-known 11-year Schwabe cycles. Solar dynamo is thought to be the
responsible mechanism for generation of the QBOs.
Aims: In this work, we analyse sunspot areas to investigate the spatial and
temporal behaviour of the QBO signal and study the responsible physical
mechanisms using simulations from fully nonlinear mean-field flux-transport
dynamos.
Methods: We investigated the behaviour of the QBOs in the sunspot area data
in full disk, and northern and southern hemispheres, using wavelet and Fourier
analyses. We also ran solar dynamos with two different approaches to generating
a poloidal field from an existing toroidal field, Babcock-Leighton and
turbulent mechanisms. We then studied the simulated magnetic field
strengths as well as meridional circulation and differential rotation rates
using the same methods.
Results: The results from the sunspot areas show that the QBOs are present in
the full disk and hemispheric sunspot areas and they show slightly different
spatial and temporal behaviours, indicating a slightly decoupled solar
hemispheres. The QBO signal is generally intermittent and in-phase with the
sunspot area data, surfacing when the solar activity is in maximum. The results
from the BL-dynamos showed that they are neither capable of generating the
slightly decoupled behaviour of solar hemispheres nor can they generate
QBO-like signals. The turbulent -dynamos, on the other hand, generated
decoupled hemispheres and some QBO-like shorter cycles.
Conclusions: In conclusion, our simulations show that the turbulent
-dynamos with the Lorentz force seems more efficient in generating the
observed temporal and spatial behaviour of the QBO signal compared with those
from the BL-dynamos
3D simulations of rising magnetic flux tubes in a compressible rotating interior: The effect of magnetic tension
Context: Long-term variability in solar cycles represents a challenging
constraint for theoretical models. Mean-field Babcock-Leighton dynamos that
consider non-instantaneous rising flux tubes have been shown to exhibit
long-term variability in their magnetic cycle. However a relation that
parameterizes the rise-time of non-axisymmetric magnetic flux tubes in terms of
stellar parameters is still missing. Aims: We aim to find a general
parameterization of the rise-time of magnetic flux tubes for solar-like stars.
Methods: By considering the influence of magnetic tension on the rise of
non-axisymmetric flux tubes, we predict the existence of a control parameter
referred as . This parameter is a measure of the
balance between rotational effects and magnetic effects (buoyancy and tension)
acting on the magnetic flux tube. We carry out two series of numerical
experiments (one for axisymmetric rise and one for non-axisymmetric rise) and
demonstrate that indeed controls the rise-time
of magnetic flux tubes. Results: We find that the rise-time follows a power law
of with an exponent that depends on the
azimuthal wavenumber of the magnetic flux loop. Conclusions: Compressibility
does not impact the rise of magnetic flux tubes, while non-axisymmetry does. In
the case of non-axisymmetric rise, the tension force modifies the force balance
acting on the magnetic flux tube. We identified the three independent
parameters required to predict the rise-time of magnetic flux tubes, that is,
the stellar rotation rate, the magnetic flux density of the flux tube, and its
azimuthal wavenumber. We combined these into one single relation that is valid
for any solar-like star. We suggest using this generalized relation to
constrain the rise-time of magnetic flux tubes in Babcock-Leighton dynamo
models.Comment: 18 pages, 15 figures, 6 tabula
Reconstruction of the Solar Activity from the Catalogs of the Zurich Observatory
Catalogs of the Zurich Observatory contain positional information on
sunspots, prominences and faculae in late 19th and early 20th centuries. This
database is given in handwritten tabular form and was not systematically
analysed earlier. It is different from the sunspot number time series made in
Zurich and was obtained with a larger telescope. We trained a neural-network
model for handwritten text recognition and present the database of
reconstructed coordinates. The database obtained connects the earlier
observations by Sp\"orer with later programs of the 20th century and
supplements the sunspot-group catalogs of the Royal Greenwich Observatory. We
also expect that the presented machine-learning approach and its deep
capabilities will motivate the processing of a wide bulk of astronomical data,
which is still given in non-digitized form or as plain scanned images
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