37 research outputs found
Karl Schwarzschild, Annie J. Cannon and Cornelis Easton:The honorary PhDs of Jacobus C. Kapteyn
Karl Schwarzschild, Annie J. Cannon and Cornelis Easton:The honorary PhDs of Jacobus C. Kapteyn
Honorary degrees and particularly doctorates are important instruments to enhance the standing of universities and professors, in addition to receiving these as a measure of a scientist's recognition. Jacobus C. Kapteyn from the University of Groningen in the Netherlands, one of the most prominent astronomers of his times, received three of these and has persuaded his university to award at least three, possibly five. I examine the background of the selection of the latter in view of developments in Kapteyn's time in his career, international astronomy and political and cultural circumstances
Karl Schwarzschild, Annie J. Cannon, and Cornelis Easton:PhDs honoris causa of Jacobus C. Kapteyn
Karl Schwarzschild, Annie J. Cannon, and Cornelis Easton:PhDs honoris causa of Jacobus C. Kapteyn
Karl Schwarzschild, Annie J. Cannon and Cornelis Easton:The honorary PhDs of Jacobus C. Kapteyn
Karl Schwarzschild, Annie J. Cannon, and Cornelis Easton:PhDs honoris causa of Jacobus C. Kapteyn
Honorary degrees and particularly doctorates are important instruments to enhance the standing of universities and professors, in addition to receiving these as a measure of a scientist's recognition. Jacobus C. Kapteyn from the University of Groningen in the Netherlands, one of the most prominent astronomers of his times, received three of these and has persuaded his university to award at least three, possibly five. I examine the background of the selection of the latter in view of developments in Kapteyn's times in his career, international astronomy and political and cultural circumstances
Automating the Synthetic Field Method:Application to Sextans A
We have automated the ``Synthetic Field Method'' developed by Gonzalez et
al.(1998) and used it to measure the opacity of the ISM in the Local Group
dwarf galaxy Sextans A by using the changes in counts of background galaxies
seen through the foreground system. The Sextans A results are consistent with
the observational relation found by Cuillandre et al. (2001) between dust
opacity and HI column density in the outer parts of M31.Comment: 4 pages, 6 figures, submitted for the proceedings of The Dynamics,
Structure and History of Galaxies: A Workshop in Honour of Prof. Ken Freema
Flattening and truncation of stellar discs in edge-on spiral galaxies
We analyse the global structure of the old stellar discs in 34 edge-on spiral
galaxies. The radial and vertical exponential scale parameters of the discs are
obtained by applying an improved two-dimensional decomposition technique to our
I-band photometry. We find a clear increase in the disc scaleheight with
maximum rotational velocity, in accordance with observations of the stellar
velocity dispersions in galaxy discs. The range and maximum of the intrinsic
flattening of the disc light seem to increase with both maximum rotational
velocity and total HI mass. We use the disc flattening to estimate the disc
contribution to the maximum rotational velocity, resulting in an average of
57+-22 percent. The disc light distributions are further investigated for the
presence of radial truncations. We find that the radial light distributions of
at least 20 spirals are truncated, corresponding to 60 percent of the sample.
For small scalelength spirals, which are the most numerous in the local
Universe, the results suggest that the average ratio of disc truncation radius
to disc scalelength is at least four.Comment: 25 pages, 7 figures, appendix, Accepted for MNRAS (April 4 2002
A new method for obtaining the star formation law in galaxies
We present a new observational method to evaluate the star formation law as
formulated by Schmidt: the power-law expression assumed to relate the rate of
star formation in a volume of space to the local total gas volume density.
Volume densities in the clouds surrounding an OB association are determined
with a simple model which considers atomic hydrogen as a photodissociation
product on cloud surfaces. The photodissociating flux incident on the cloud is
computed from the far-UV luminosity of the OB association and the geometry. We
have applied this "PDR Method" to a sample of star-forming regions in M33 using
VLA 21-cm data for the HI and GALEX imagery in the far-UV. It provides an
estimate of the total volume density of hydrogen (atomic + molecular) in the
gas clouds surrounding the young star cluster. A logarithmic graph of the
cluster UV luminosity versus the surrounding gas density is a direct measure of
the star formation law. However, this plot is severely affected by
observational selection, rendering large areas of the diagram inaccessible to
the data. An ordinary least-squares regression fit therefore gives a strongly
biased result. Its slope primarily reflects the boundary defined when the 21-cm
line becomes optically thick, no longer reliably measuring the HI column
density. We use a maximum-likelihood statistical approach which can deal with
truncated and skewed data, taking into account the large uncertainties in the
derived total gas densities. The exponent we obtain for the Schmidt law in M33
is 1.4 \pm 0.2.Comment: Accepted for publication in Ap
IAU Commission C3 (History of Astronomy): Triennial Report, 2018–2021
IAU Commission C3 (History of Astronomy) started in 2015 as a natural continuation of the previous IAU Commission 41 for History of Astronomy which was established in 1948 and which was extremely successful in supporting research on the history of astronomy, organizing and sponsoring workshops and conferences, promoting research collaborations, forming specialist working groups and fostering the publication of members' research (see Kochhar et al., 2015)