Author name code: al
ADS astronomy entries on 2022-09-14
=author:"Al, N." OR =author:"Al, Nurol" OR =author:"Al Erdogan, N."
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Title: Oscillatory behaviour of chromospheric fine structures in a
network and a semi-active region
Authors: Bostancı, Zahide Funda; Gültekin, Asuman; Al, Nurol
Bibcode: 2014MNRAS.443.1267B
Altcode: 2014arXiv1406.4507B
In this work, we study the periodicities of oscillations in dark fine
structures using observations of a network and a semi-active region
close to the solar disc centre. We simultaneously obtained spatially
high-resolution time series of white light images and narrow-band images
in the Hα line using the 2D Göttingen spectrometer, which were based
on two Fabry-Perot interferometers and mounted in the Vacuum Tower
Telescope/Observatorio del Teide/Tenerife. During the observations,
the Hα line was scanned at 18 wavelength positions with steps of 125
mÅ. We computed series of Doppler and intensity images by subtraction
and addition of the Hα ± 0.3 Å and ± 0.7 Å pairs, sampling the
upper chromosphere and the upper photosphere, respectively. Then, we
obtained power, coherence and phase difference spectra by performing
a wavelet analysis to the Doppler fluctuations. Here, we present
comparative results of oscillatory properties of dark fine structures
seen in a network and a semi-active region.
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
Bibcode: 2012AN....333..880P
Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.
Title: A study about the solar chromosphere above photospheric
bright points
Authors: Gültekin, Asuman; Funda Bostanci, Zahide; Al, Nurol
Bibcode: 2012cosp...39.2287G
Altcode: 2012cosp.meet.2287G
In this work, we study the oscillatory behaviour of the solar
chromosphere above photospheric bright points lying in a semi-active
region. For this purpose, we use spatially high resolution time series
of white light images and narrow band filtergrams, which were taken
simultaneously. These filtergrams were taken by scanning the Halpha line
profile at 18 wavelength points using a two-dimensional spectrometer,
which was mounted at the Gottingen Vacuum Tower Telescope. Using the
lambdameter method we compute two-dimensional intensity and Doppler
images for several line depths. Applying the Fourier analysis, we get
power spectra for different height levels of the solar chromosphere
above the bright points. Our aim is to reveal whether there is a
relationship between the bright points and the periodic behaviour of
the solar chromosphere, or not.
Title: Cloud modeling of a quiet solar region in Halpha .
Authors: Bostanci, Z. F.; Al Erdoğan, N.
Bibcode: 2010MmSAI..81..769B
Altcode: 2010arXiv1001.3361B
We present chromospheric cloud modeling on the basis of Halpha
profile-sampling images taken with the Interferometric Bidimensional
Spectrometer (IBIS) at the Dunn Solar Telescope (DST). We choose the
required reference background profile by using theoretical NLTE profile
synthesis. The resulting cloud parameters are converted into estimates
of physical parameters (temperature and various densities). Their mean
values compare well with the VAL-C model.
Title: Physical Parameters of a Rosette Observed in H-alpha
Authors: Al Erdogan, N.; Bostanci, Z. F.; Gultekin, A.
Bibcode: 2008ESPM...12.2.29A
Altcode:
In May 2002, the solar chromosphere was observed in H? with the
two-dimensional 'Gottingen' Fabry-Perot spectrometer which is mounted
in the German Vacuum Tower Telescope (VTT) at the Observatorio del
Teide/Tenerife. The data consist of broad-band and narrow-band images
which were taken by scanning through this line. For a short period of
this time series, we calculated the source function, the line-of-sight
velocity, the Doppler width and the optical depth using Becker's cloud
model. We also estimated the number densities and the temperature of
the structure under investigation. Here, we present several results
of this study.
Title: 2D Observation of a Small Active Region in Hα
Authors: Gültekin, A.; Bostanci, Z. F.; Al Erdogan, N.
Bibcode: 2007ASPC..368..119G
Altcode:
A small active region on the solar chromosphere was observed with
high spatial and spectral resolution in Hα. The data were obtained
with the Göttingen Fabry-Pérot Spectrometer mounted in the Vacuum
Tower Telescope at the Observatorio del Teide in May 2002. Intensity
and velocity maps for different line widths were derived over the
two-dimensional field of view by applying the Lambdameter method. Some
physical parameters like the source function, the line-of-sight
velocity, the Doppler width, and the optical depth of fibril-like
structures were determined using Beckers' cloud model. First results
of this study are presented.
Title: Dynamics of an enhanced network region observed in Hα
Authors: Al, N.; Bendlin, C.; Hirzberger, J.; Kneer, F.; Trujillo
Bueno, J.
Bibcode: 2004A&A...418.1131A
Altcode:
This investigation is based on Hα observations of high spatial
resolution. They stem from an enhanced network region near disk centre
of the sun and consist of broad-band and narrow-band images taken with
the two-dimensional ``Göttingen'' Fabry-Perot spectrometer mounted in
the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. The
``lambdameter method'' was applied to derive intensity and velocity
maps over the two-dimensional field of view reflecting the behaviour
of these parameters in the solar chromosphere. The determination of
the source function, the line-of-sight (LOS) velocity, the Doppler
width and the optical depth was based on Beckers' cloud model
(Beckers \cite{beckers}). From the LOS velocity distribution along
the Hα structures we conclude that ballistic motions are unlikely to
prevail. Especially the bright Hα features cannot be explained by the
cloud model. It is shown how, instead, two-dimensional non-LTE radiative
transfer calculations of embedded chromospheric structures lead to
reasonable agreement with the observed line profiles from these bright
features. It is found that many of the bright fibril-like structures
near dark fibrils can be explained by radiation which is blocked by
absorbing material at large heights and escapes through less opaque
regions. We estimate the number densities and the temperature. With
these and with the measured velocities, the kinetic energy flux and
the enthalpy flux related to the motions of the fine structures can
be calculated. Both fall short by at least an order of magnitude of
covering energy losses by radiation of active chromospheric regions.
Title: Dynamics of Solar Chromospheric Finestructures in H-alpha
observed with High Spatial Resolution
Authors: Al, Nurol; Kneer, Franz; Hirzberger, Johann
Bibcode: 2003ANS...324..111A
Altcode: 2003ANS...324..P17A
No abstract at ADS
Title: Two-dimensional speckle spectroscopy of Hα features
Authors: Al, N.; Hirzberger, J.; Kneer, F.
Bibcode: 2003AN....324..364A
Altcode:
In May 2002, the solar chromosphere was observed with a two-dimensional
spectrometer which is mounted in the German Vacuum Tower Telescope (VTT)
at the Observatorio del Teide/Tenerife. The aim of this observation was
to investigate the fine structure of the solar chromosphere seen in Hα
. We took narrow-band filtergrams (Delta lambda ~ 72 mÅ) by scanning
through this line. Broad-band images taken strictly simultaneously
with the narrow-band filtergrams were restored by speckle methods. The
instantaneous optical transfer function from this restoration procedure
was used for the reconstruction of the narrow-band images. Some results
of this high spatial resolution observation are presented below.
Title: A Fabry-Perot spectrometer for high-resolution observation
of the Sun
Authors: Kneer, F.; Al, N.; Hirzberger, J.; Nicklas, H.; Puschmann,
K. G.
Bibcode: 2003AN....324..302K
Altcode:
No abstract at ADS
Title: Does the sun affect the earth's climate?
Authors: Kilçik, A.; Ökten, A.; Al, N.
Bibcode: 2002ESASP.477..559K
Altcode: 2002scsw.conf..559K
In this study, we deal with the question whether the solar activity
affects the earth's climate or not. For this reason, we have chosen
two parameters to check a possible relation, the total size of Ca
plage areas on the sun and terrestrial air temperatures above the
ground at more than 1300 stations covering the northern latitude belt
between 30 and 60 degrees. Data include the time period between 1940
and 1984. We found a strong positive correlation between the two
parameters up to 1966, but after this time an anti-correlation was
seen. In the investigated period the mean value of temperature was
10.56+/-0.32°C. Our investigation shows that an effect of the sun
upon the earth's atmosphere seems to exist, but increasing amounts of
greenhouse gases (GHGs) dominate the solar influence.
Title: Dynamics of small features in the solar chromosphere
Authors: Al, N.; Bendlin, C.; Kneer, F.
Bibcode: 2002A&A...383..283A
Altcode:
A spatially highly resolved time series of a quiet region at disk
centre taken in the Na D_2 line with the ``Göttingen'' spectrometer
in the Vacuum Tower Telescope/Tenerife was used to study the dynamic
behaviour of different chromospheric features. Two CCDs were employed
for simultaneous exposures of narrow-band and ``white-light'' images
forming 128 repetitive ``scans'' of 30 images each in nearly two
hours. The data set yielded line profiles over the two-dimensional field
of view which served to create various maps indicating, e.g., vertical
velocities or minimum line intensities. The analysis of the features of
interest was further based on maps displaying the horizontal velocity
field derived from white-light images. The occurrence of various
bright points was monitored, showing quite different properties. Some
persistent intra-network bright points follow the horizontal flows of
the underlying photosphere. During the time series, a ``K grain'' is
seen to occur several times at the same location. The power spectrum
of the fluctuation of the minimum intensity of its corresponding Na
D_2 mean line profile exhibits a pronounced absolute maximum for a
period of about 24 min. The behaviour of several peculiar intra-network
bright points still lacks an unequivocal interpretation. Possibly, the
signature of gravity waves has been detected. Further investigation
revealed that the power spectra of the fluctuation of Doppler shift
and minimum intensity calculated for one of these bright points both
show an absolute maximum for a period of 4.3 min. In the course of
these fluctuations, time spans of regular oscillations were noticed
for all such points lasting from about 15 to 25 min. Power spectra
calculated only over these times exhibit pronounced absolute maxima
in a rather narrow frequency range.
Title: Eclipse observations of Istanbul University observatory and
Abastumani astrophysical observatory
Authors: Ökten, A.; Özkan, M. T.; Özýpýk, T.; Ak, T.; Gülseçen,
H.; Al, N.; Saygac, A. T.; Gülseçen, S.; Esenoǧlu, H.; Kýlçýk,
A.; Kara, M.; Kulijanisvili, V. I.; Gigolashvili, M. Sh.; Ambartsumian,
A. An.; Khetsuriani, Ts. T.; Borchkhadze, T. M.; Khutsisvili, E. V.;
Goderidze, E. K.; Kiladze, R. I.; Japiashvili, V. P.; Salukvadze,
G. N.; Gheonjan, L. A.; Javkhisvili, G. O.; Mayer, A.; Japaridze,
D. R.; Kapanadze, Z.; Dernedjiev, V. N.
Bibcode: 2002frte.conf...30O
Altcode:
To find the solar coronal structural propertiesusingthe oportinity
of total solar eclipse event, we have organized an expedition at two
stations separated from each other about 400 km. Both stations were
very close to the center line. We, both Istanbul University Observatory
and Abastumani Astrophysical Observatorymembers, have performed total
fourteen experiments. These are related to the following topics: white
light corona, chromospheric structures, coronal polar plumes; solar
diameter measurements and photoelectric polarimetric measurements. Some
preliminary results about white light polarisation and polar plume
observations are presented in these Proceedings. Other reductions are
still proceeding.
Title: The sunspot observations made in 1997
Authors: Kilcik, Ali; Al, Nurol
Bibcode: 2001IsJAP..63...57K
Altcode:
In the photospheric observations made at the Istanbul Univercity
Observatory, observable sunspot and faculae are drawn on a projected
disk of the Sun and the heliographic coordinates of the sunspots are
determined from these dravings.
Title: Objectives of the Georgian-Turkish Joint Group at Solar
Eclipse in Elazig
Authors: Gigolashvili, M. Sh.; Khetsuriani, Ts. S.; Khutsishvili,
E. V.; Kiladze, R. I.; Salukvadze, G. N.; Gheonjan, L. A.; Mayer,
A. K.; Japaridze, D. R.; Kapanadze, Z.; Ökten, A.; Özkan, T.;
Özisik, T.; Gülseçen, H.; Al, N.; Gülseçen, S.; Kilçik, A.;
Özgür, B.; Bostanci, F.
Bibcode: 2000ASPC..205..190G
Altcode: 2000ltse.conf..190G
Bougaziçi University, Kandilli Observatory and Earthquake Research
Institute and Astronomical Institute of the Slovak Academy of Sciences
organized collaborative expeditions for the August 11, 1999 total
solar eclipse in Turkey and in Hungary. In these expeditions some five
experiments were carried out associated with the white-light inner
and outer corona, coronal polarization and high resolution imaging
of helmety streamers. Here we present what we could do through out
the programs.
Title: Erratum: Two-dimensional spectroscopic observations of
chromospheric oscillations
Authors: Al, Nurol; Bendlin, Cornelia; Kneer, Franz
Bibcode: 1999A&A...342..311A
Altcode:
For technical reasons, Figs. ref{f8} and ref{f9} were printed with
incorrect colour separation. To rectify this unfortunate error, the
correct Figs. ref{f8} and ref{f9} with the captions are reprinted below.
Title: Some remarkable bright points seen in the Na D2
line.
Authors: Al, N.; Bendlin, C.; Kneer, F.
Bibcode: 1999joso.proc..133A
Altcode:
A spatially highly resolved time series of the solar chromosphere
was taken with a two-dimensional spectrometer mounted in the German
Vacuum Tower Telescope (VTT) on Tenerife. The authors obtained
narrow-band filtergrams (Δλ = 30 mÅ) and white-light images strictly
simultaneously with two CCDs. Repetitive tuning of a Fabry-Perot
interferometer allowed to scan through the Na D2 line (5890
Å) in short intervals. In this contribution, the authors focus on
bright points in the intra-network using different diagnostic tools
to study their temporal and oscillatory behaviour.
Title: Two-dimensional spectroscopic observations of chromospheric
oscillations
Authors: Al, Nurol; Bendlin, Cornelia; Kneer, Franz
Bibcode: 1998A&A...336..743A
Altcode:
The oscillatory behaviour of the solar chromosphere was studied
from observations of a quiet region at disk centre using various
diagnostic tools. The two-dimensional spectrometer in the Vacuum Tower
Telescope/Tenerife (Spain) served to obtain a spatially highly resolved
time series of ``white-light'' images and narrow-band filtergrams in
the Na D_2 line. With a tunable Fabry-Perot interferometer, this line
was scanned taking 30 images (i.e. a ``scan'') around the line core
with wavelength steps of 30 m Angstroms and a spectral resolution
of about 200 000. From these images, line profiles were derived for
every pixel in the field of view. With each such narrow-band scan, a
scan of ``white-light'' images was taken strictly simultaneously. The
whole time series comprises (2x) 128 scans. Every 56 s, a new pair of
scans was started with two CCDs, thus the observation covers nearly
two hours. Finally, after correlation and other reduction procedures,
a field size of 69\farcs4 x 50\farcs4 remained with 0\farcs2/pixel
on the CCD-chips. In the data reduction, new images were created
representing the minimum intensity (I) of each line profile in the
field of view, and also velocity (V) maps (derived from the Doppler
shifts of the line profiles) for all 128 scans. >From these images,
power spectra and diagnostic diagrams were computed. In the subsequent
analysis, a distinction between network and intra-network regions was
made where this seemed appropriate. One- and two-dimensional (V-I) phase
and coherence spectra were analysed with regard to oscillations and to
the nature of the waves leaving their marks in these diagrams. Several
noteworthy results also raised the question of the actual line formation
height of Na D_2, among them being the non-detection of a chromospheric
eigenmode. While an explanation for a conspicuous 70(deg) plateau in a
small region of the phase spectra already exists, the suspected reason
behind the decreasing phase difference from about -60(deg) for the
f-mode down to ~ -120(deg) for higher modes is still subject to some
speculation. Moreover, the data gave evidence of gravity waves, probably
discovered for the first time in a V-I phase spectrum of Na D_2.
Title: Dynamics of Solar Fine Structure: Observation with High
Spatial Resolution
Authors: Al, N.; Bendlin, C.; de Boer, C. R.; Denker, C.; Kneer, F.;
Schmitt, D.; Volkmer, R.; Wilken, V.
Bibcode: 1998ASPC..154..553A
Altcode: 1998csss...10..553A
The Sun is an ideal object for studying non-magnetic and magnetic
processes in cool stars. Here, we focus on fine structures of a
few 100 km in the solar atmosphere. Granular overshoot, motions
and waves of magnetic elements in the quiet Sun and in plages,
etc., all affect the atmospheric structure from the bottom of the
photosphere up to the corona and the solar wind. Observations with
high spatial resolution are required to reveal the dynamic behaviour
and to understand the underlying physical processes. During the past
five years, speckle methods have become an excellent tool to obtain
images of solar fine structure with diffraction-limited resolution. We
demonstrate by some examples how one can gain new insights from
speckle interferometry. Likewise, spectroscopy of solar fine structure
is also making rapid progress towards high spatial resolution. Our
two-dimensional, narrow-band spectrometer (Delta\lambda = 20-30 mAA
), working with a scanning Fabry-Perot interferometer, proves very
powerful in several aspects. We present some results obtained in Na D_2
from the quiet solar chromosphere. Using suitable observing techniques
together with image restoration, we aim at achieving diffraction-limited
resolution also for narrow-band spectroscopy.