POSSIBLE OBSERVING PROJECTS (under construction)
Astronomy C3646
OBSERVATIONAL ASTRONOMY
Instructor:
Arlin Crotts
Professor of Astronomy
Phone number: 854-7899
Office: Pupin 1012
e-mail: arlin
astro.columbia.edu
Here are a few possible observing projects, with more to follow:
Galaxies in the Kepler space telescope field
We will use existing images from the Palomar Transient Factory (using the
48-inch Oschin schmidt telescope on Mt. Palomar, California) to locate
previously unidentified galaxies in the field of the Kepler space telescope
and classify them by color and galaxy type.
In January we will be able to propose to observe these with the Kepler and
measure how the nuclei of galaxies vary in brightness (due to their central
black holes, primarily) at levels that are much more sensitive than previously
explored.
In the meantime we can see how galaxy counts vary with Galactic Latitude, and
measure if dimming due to galactic extinction by dust acts as predicted.
These results can be supplemented for fainter galaxies by data to be obtained
from the MDM 2.4-meter telescope.
Color-Magnitude Diagram of the Pleiades cluster
By measuring the brightness and color of a cluster of stars at the same
distance we can measure their age and composition, along with other details.
This involves taking a few images of the brightest stars in the Pleiades from
the Pupin rooftop with the equipment there, and can be supplemented for fainter
star with the MDM 2.4-meter telescope.
Spectroscopic ages of Pleiades cluster stars, with Marcel Agueros
A star's age is one of its most fundamental parameters but notoriously
difficult to measure accurately for individal star.
Andrew Skumanich proposed that rotation and chromospheric activity, a proxy for
magnetic field strength, decrease at roughly the same rate for stars like the
Sun between the ages of 100 and 500 Myr.
The existence of a potential relationship between age, rotation, and activity
has generated hope that measurements of rotation or activity can be used to
infer the ages of field (non-cluster) stars.
Unfortunately, the theoretical underpinnings of the age-rotation and
age-activity relations are still poorly understood, and empirical measurements
of these relations are somewhat limited. As a result, astronomers still
struggle to answer that simplest of questions: how old is that star?
We have a campaign with MDM to obtain spectra for stars of known ages for which
we have attempted to measure rotation periods. Measurements of the Halpha
emission lines in these spectra will allow us to calibrate the age-activity and
rotation-activity relations, thereby improving our stellar chronometers.
This project involves two phases:
(1) reducing and analyzing existing MDM 1.3-meter spectra for stars in the Pleiades open cluster (roughly 120 Myr old), and
(2) obtaining, reducing, and analyzing new MDM 2.4-meter spectra for Pleiades
and Alpha Persei (35 Myr old) stars.
Mass-to-light ratio of different galaxy types
We learned four decades ago that galaxies are dominated by mass in a form we
cannot see.
This is expressed in the "mass-to-light" ratio, compared to that quantity for
populations of stars.
We can measure the mass by measuring the internal velocities of galaxies as a
function of radius, primarily by the measuring the rotation velocity versus
radius ("rotation curve").
The amount of light is measured from optical images, using different
wavelengths to estimate the loss due to extinction of light by dust.
This require images and spectra to be obtained at the MDM 2.4-meter telescope.
Variable Star Projects, with Joe Patterson
We receive photometric data daily from telescopes scattered around the world
(the Center for Backyard Astrophysics: cba.phys.columbia.edu).
Most of this is time-series photometry -- typically 30 s integrations, all
night long, of cataclysmic variables and other close binary stars.
The over-arching goal is an understanding of how close binaries end their
lives.
But in the process we have been drawn into some other fascinating byways:
(1) Precession of accretion disks.
We now find nearly all of the world's supply of such things (about 100), and
measure their periods;
(2) Measurement of orbital period changes in close binaries.
In most cases these are too small to measure in a few decades.
But in the stars of highest mass loss rate, the supersoft binaries, we do
measure them -- and hence obtain a direct measure of their evolution rate;
(3) Discovery of accreting, rapidly rotating magnetic white dwarfs -- the DQ
Herculis stars;
(4) Discovery of "period bouncers" -- the oldest cataclysmic variable stars in
the Galaxy;
(5) Measurement of periods and masses in the AM CVn stars: double white dwarfs
where the more massive is cannibalizing the less massive.
With orbital periods of ~20 min and likely powered purely by gravitational
radiation, these binaries are likely to be strongly detected by the coming
generation of gravitational-wave detectors.
They may become the principal calibrators of these detectors.
Optical Imaging and Spectroscopy of Cataclysmic Variable Stars and Other
Compact Objects, with Jules Halpern
This involves existing images and spectra plus more data to be collected from
the MDM 2.4-meter.
We need to consult with Prof. Halpern for a better description.
Radio Interferometric Mapping, with Jacqueline van Gorkom
This involves existing radio telescope array data.
We need to consult with Prof. van Gorkom for a better description.
X-Ray Imaging and Spectroscopy of Active Galactic Nuclei and Other
Extragalactic Objects, with Frits Paerels
This involves existing X-ray satellite telescope data.
We need to consult with Prof. Paerels for a better description.
2012 September 10
