Kapteyn Institute Preprints (1999)
Kapteyn Institute Preprint Service.
Preprints of the Kapteyn Institute.
Paper copies can be ordered at:
Kapteyn Institute
P.O. Box 800
9700 AV Groningen
The Netherlands
All the preprints are compressed using gzip.
1999 Preprints
-
Preprint 290
Detection Efficiencies of Microlensing Datasets to
Stellar and Planetary Companions
B. Scott Gaudi and Penny D. Sackett
-
Preprint 289
Astrometric Microlensing of Stars
M. Dominik, K.C. Sahu
-
Preprint 288
The discovery of a microarcsecond quasar: J1819+3845
J. Dennett-Thorpe, A.G. de Bruyn
-
Preprint 287
Combined Analysis of the Binary-Lens Caustic-Crossing Event
MACHO 98-SMC-1
: C. Afonso, C. Alard, J.N. Albert, J. Andersen, R. Ansari,
E. Aubourg, P. Bareyre, F. Bauer, J.P. Beaulieu, A. Bouquet,
S. Char, X. Charlot, F. Couchot, C. Coutures, F. Derue,
R. Ferlet, J.F. Glicenstein, B. Goldman, A. Gould, D. Graff,
M. Gros, J. Haissinski, J.C. Hamilton, D. Hardin, J. de Kat,
A. Kim, T. Lasserre, E. Lesquoy, C. Loup, C. Magneville,
J.B. Marquette, E. Maurice, A. Milsztajn, M. Moniez,
N. Palanque-Delabrouille, O. Perdereau, L. Prevot, N. Regnault,
J. Rich, M. Spiro, A. Vidal-Madjar, L. Vigroux, S. Zylberajch
(The EROS Collaboration),
C. Alcock, R.A. Allsman, D. Alves, T.S. Axelrod, A.C. Becker,
K.H. Cook, A.J. Drake, K.C. Freeman, K. Griest, L.J. King,
M.J. Lehner, S.L. Marshall, D. Minniti, B.A. Peterson,
M.R. Pratt, P.J. Quinn, A.W. Rodgers, P.B. Stetson, C.W. Stubbs,
W. Sutherland, A. Tomaney, T. Vandehei
(The MACHO/GMAN Collaboration),
S.H. Rhie, D.P. Bennett, P.C. Fragile, B.R. Johnson, J. Quinn
(The MPS Collaboration),
A. Udalski, M. Kubiak, M. Szymanski, G. Pietrzynski, P. Wozniak,
K. Zebrun
(The OGLE Collaboration),
M.D. Albrow, J.A.R. Caldwell, D.L. DePoy, M. Dominik, B.S.
Gaudi,
J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies, R.M.
Naber,
R.W. Pogge, K.R. Pollard, P.D. Sackett, K.C. Sahu, P. Vermaak,
R. Watson, A. Williams
(The PLANET Collaboration)
-
Preprint 286
Radio imaging of core-dominated high redshift quasars
Peter D. Barthel, Marianne Vestergaard, and Colin J. Lonsdale
-
Preprint 285
A Complete Set of Solutions For Caustic-Crossing Binary
Microlensing Events
M. D. Albrow, J.-P. Beaulieu, J. A. R. Caldwell, D. L. DePoy,
M. Dominik, B. S. Gaudi, A. Gould, J. Greenhill, K. Hill, S.
Kane,
R. Martin, J. Menzies, R. M. Naber, R. W. Pogge, K. R. Pollard,
P. D. Sackett, K. C. Sahu, P. Vermaak, R. Watson, A. Williams
(The PLANET Collaboration)
-
Preprint 284
Detection of Warm and Cold Phases of the Neutral ISM in a Damped
Ly-alpha Absorber
W.M. Lane, F.H. Briggs, and A. Smette
-
Preprint 283
ISO-SWS observations of interstellar solid 13CO2: heated ice
and the Galactic 12C/13C abundance ratio
A.C.A. Boogert, P. Ehrenfreund, P.A. Gerakines, A.G.G.M. Tielens,
D.C.B. Whittet, W.A. Schutte, E.F. van Dishoeck,
Th. de Graauw, L. Decin, T. Prusti
-
Preprint 282
The Planetary Nebulae Spectrograph
M. Arnaboldi, M. Capaccioli, N. Douglas, K. Kuijken, K. Freeman,
T. Axelrod, K. Taylor, R. Gilmozzi and R. Kudritzki
-
Preprint 281
Neutral hydrogen and dark matter in spiral galaxies
Renzo Sancisi
-
Preprint 280
On the axis ratio of the stellar velocity ellipsoid in disks
of spiral galaxies
P.C. van der Kruit and R. de Grijs
-
Preprint 279
Properties of the Stellar Velocity Ellipsoid and Stability in
Disks of Spiral Galaxies
P.C. van der Kruit
-
Preprint 278
The Milky Way compared to external galaxies
P.C. van der Kruit
-
Preprint 277
The binary gravitational lens and its extreme cases
M. Dominik
-
Preprint 276
Lensed galaxies in Abell 370. II. The ultraviolet properties
of arclets and the star formation rate at high redshift
J. Bezecourt, G. Soucail, R.S. Ellis, J.-P. Kneib
-
Preprint 275
Lensed galaxies in Abell 370. I. Modeling the number counts and
redshift distribution of background sources
J. Bezecourt, J.P. Kneib, G. Soucail, T.M.D. Ebbels
-
Preprint 274
Surface photometry of bulge dominated low surface brightness
galaxies
M. Beijersbergen, W.G.J. de Blok, and J.M. van der Hulst
-
Preprint 273
Spectrophotometry of nearby field galaxies: the data,
R.A. Jansen, D. Fabricant, M. Franx, N. Caldwell
-
Preprint 272
Surface photometry of nearby field galaxies: the data,
R.A. Jansen, M. Franx, D. Fabricant, N. Caldwell
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Preprint 271
Planetary Microlensing: Present Status and Long-term Goals,
Penny D. Sackett
-
Preprint 270
Galaxy kinematics from counter-dispersed imaging,
N.G. Douglas, K. Taylor
-
Preprint 269
The kinematics of the bulge and the disc of NGC 7331,
Roelof Bottema
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Preprint 268
Limb-Darkening of a K Giant in the Galactic Bulge:
PLANET Photometry of MACHO 97-BLG-28,
M.D. Albrow, J.-P. Beaulieu, J.A.R. Caldwell, M. Dominik,
J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies,
R.M. Naber, J.-W. Pel, K. Pollard, P.D. Sackett, K.C. Sahu,
P. Vermaak, R. Watson, A. Williams (The PLANET Collaboration),
and M. S. Sahu
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Preprint 267
The Shape of Dark Matter Halos,
Penny D. Sackett
Detection Efficiencies of Microlensing Datasets to
Stellar and Planetary Companions
B. Scott Gaudi and Penny D. Sackett
Preprint no. 290
Accepted for publication in The Astrophysical
Journal (Jan. 2000).
Abstract
Microlensing light curves are now being monitored
with the temporal sampling and photometric precision required
to detect small perturbations due to planetary companions of the primary
lens. Microlensing is complementary to other planetary
search techniques, both in the mass and orbital separation of the
planets to
which it is sensitive and its potential for measuring the
abundance of planets beyond the solar neighborhood.
We present an algorithm to analyze the efficiency with which
the presence of lensing binaries of given mass ratio
and angular separation can be detected in observed microlensing
datasets;
such an analysis is required in order to draw
statistical inferences about lensing companions.
Our method incorporates the actual sampling, photometric precision,
and monitored duration of individual light curves.
We apply the method to simulated (but realistic) data to explore
the dependence of detection efficiencies on observational parameters,
the impact parameter of the event, the finite size of the background
source,
the amount of unlensed (blended) light, and the criterion used to
define a detection. We find that:
(1) the detection efficiency depends strongly on the impact
parameter of the monitored event,
(2) the detection efficiency is robust to changes in
detection criterion for strict criteria
(Delta(chi^2) greater than ~100) and
large mass ratios (q greater than ~0.01),
(3) finite sources can dramatically alter detection efficiencies to
companions with mass ratios q less than ~0.001, and
(4) accurate determination of the blended light fraction
is crucial for the accurate determination of the
detection efficiency of individual events.
Suggestions are given for addressing complications associated with
computing
accurate detection efficiences of observed datasets.
Astrometric Microlensing of Stars
M. Dominik, K.C. Sahu
Preprint no. 289
Accepted for publication in The Astrophysical
Journal.
Abstract
Due to dramatic improvements in the precision of astrometric
measurements, the observation of light centroid shifts
in observed stars due to
intervening massive compact objects ('astrometric microlensing') will
become possible in the near future. Upcoming space missions, such as SIM
and GAIA, will provide measurements with an accuracy of 4-60 micro-as
depending on the magnitude of the observed stars, and an accuracy of
~1 micro-as is expected to be achieved in the more distant future. There
are two different ways in which astrometric microlensing signals can be
used to infer information: one possibility is to perform astrometric
follow-up observations on photometrically detected microlensing events,
and the other is to perform a survey based on astrometric observations
alone. After the predictable effects of the Sun and the planets, stars in
the Galactic disk play the dominant role in astrometric microlensing. The
probability that the disk stars introduce a centroid shift larger than the
threshold deltaT at a given time for a given source in the Galactic bulge
towards Baade's window reaches 100% for a threshold of deltaT = 0.7
micro-as, while this probability is ~2% for deltaT = 5 micro-as. However,
this centroid shift does not vary much during the time in which a typical
photometric microlensing event differs from baseline. So astrometric
follow-ups (e.g. with SIM) are not expected to be disturbed by the
statistical astrometric microlensing due to disk stars, so that it is
possible to infer additional information about the nature of the lens that
caused the photometric event, as suggested. The probability to observe
astrometric microlensing events within the Galaxy turns out to be large
compared to photometric microlensing events. The probability to see a
variation by more than 5 micro-as within one year and to reach the closest
angular approach between lens and source is ~10-4 for a bulge star
towards Baade's window, while this reduces to ~6x10-6 for a direction
perpendicular to the Galactic plane. For the upcoming mission GAIA, we
expect ~1000 of the observed stars to show a detectable astrometric
microlensing signal within its 5 year lifetime. These events can be used
to determine accurate masses of the lenses, and to derive the mass and the
scale parameters (length and height) of the Galactic disk.
The discovery of a microarcsecond quasar: J1819+3845
J. Dennett-Thorpe, A.G. de Bruyn
Preprint no. 288
Accepted for publication in Astronomy and Astrophysics.
Abstract
We report on the discovery of a source which exhibits over 300%
amplitude changes in radio flux density on the period of hours. This
source, J 1819+3845, is the most extremely variable extragalactic source
known in the radio sky. We believe these properties are due to
interstellar scintillation, and show that the source must emit at least
55% of its flux density within a radius of <16 microarcseconds at 5 GHz.
The apparent brightness temperature is >5.1012 K, and the
source may be explained by a relativistically moving source with a
Doppler factor ~15. The scattering occurs predominantly in material only
a few tens of parsecs from the earth, which explains its unusually
rapid variability. If the source PKS 0405-385 (Kedsiora-Chudszer et al
1997 is similarly affected by local scattering material, Doppler factors
of ~ 10000 are not required to explain this source. The discovery of a
second source whose properties are well modeled by interstellar
scintillation strengthens the argument for this as the cause for much of
the variations seen in intra-day variables (IDV).
Combined Analysis of the Binary-Lens Caustic-Crossing Event
MACHO 98-SMC-1
C. Afonso, C. Alard, J.N. Albert, J. Andersen, R. Ansari,
E. Aubourg, P. Bareyre, F. Bauer, J.P. Beaulieu, A. Bouquet,
S. Char, X. Charlot, F. Couchot, C. Coutures, F. Derue,
R. Ferlet, J.F. Glicenstein, B. Goldman, A. Gould, D. Graff,
M. Gros, J. Haissinski, J.C. Hamilton, D. Hardin, J. de Kat,
A. Kim, T. Lasserre, E. Lesquoy, C. Loup, C. Magneville,
J.B. Marquette, E. Maurice, A. Milsztajn, M. Moniez,
N. Palanque-Delabrouille, O. Perdereau, L. Prevot, N. Regnault,
J. Rich, M. Spiro, A. Vidal-Madjar, L. Vigroux, S. Zylberajch
(The EROS Collaboration),
C. Alcock, R.A. Allsman, D. Alves, T.S. Axelrod, A.C. Becker,
K.H. Cook, A.J. Drake, K.C. Freeman, K. Griest, L.J. King,
M.J. Lehner, S.L. Marshall, D. Minniti, B.A. Peterson,
M.R. Pratt, P.J. Quinn, A.W. Rodgers, P.B. Stetson, C.W. Stubbs,
W. Sutherland, A. Tomaney, T. Vandehei
(The MACHO/GMAN Collaboration),
S.H. Rhie, D.P. Bennett, P.C. Fragile, B.R. Johnson, J. Quinn
(The MPS Collaboration),
A. Udalski, M. Kubiak, M. Szymanski, G. Pietrzynski, P. Wozniak,
K. Zebrun
(The OGLE Collaboration),
M.D. Albrow, J.A.R. Caldwell, D.L. DePoy, M. Dominik, B.S.
Gaudi,
J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies, R.M.
Naber,
R.W. Pogge, K.R. Pollard, P.D. Sackett, K.C. Sahu, P. Vermaak,
R. Watson, A. Williams
(The PLANET Collaboration)
Preprint no. 287
Accepted for publication in the Astrophysical Journal, Vol. 532 (March 2000).
Abstract
We fit the data for the binary-lens microlensing event
MACHO 98-SMC-1 from 5 different microlensing collaborations and find
two distinct solutions characterized by binary separation d and mass
ratio q: (d,q)=(0.54,0.50) and (d,q)=(3.65,0.36), where d is in units of
the Einstein radius. However, the relative proper motion of the lens is
very similar in the two solutions, 1.30 km/(s kpc) and 1.48 km/(s kpc),
thus confirming that the lens is in the Small Magellanic Cloud. The
close
binary can be either rotating or approximately static but the wide
binary
must be rotating at close its maximum allowed rate to be consistent with
all the data. We measure limb-darkening coefficients for five bands
ranging from I to V. As expected, these progressively decrease with
rising
wavelength. This is the first measurement of limb darkening for a
metal-poor A star.
Radio imaging of core-dominated high redshift quasars
Peter D. Barthel, Marianne Vestergaard, and Colin J. Lonsdale
Preprint no. 286
Accepted for publication in the Astronomy and Astrophysics.
Abstract
VLA imaging at kiloparsec-scale resolution of sixteen core-dominated
radio-loud QSOs is presented. Many objects appear to display variable
radio emission and their radio morphologies are significantly smaller
than those of steep-spectrum quasars, consistent with these objects
being observed at sight lines close to their (relativistic, gamma~4-7)
jet axes. The usefulness of the radio source orientation
indicator R_V, being defined as ratio of radio core and rest
frame optical V-band luminosity, is confirmed.
A Complete Set of Solutions For Caustic-Crossing Binary
Microlensing Events
M. D. Albrow, J.-P. Beaulieu, J. A. R. Caldwell, D. L. DePoy,
M. Dominik, B. S. Gaudi, A. Gould, J. Greenhill, K. Hill, S.
Kane,
R. Martin, J. Menzies, R. M. Naber, R. W. Pogge, K. R. Pollard,
P. D. Sackett, K. C. Sahu, P. Vermaak, R. Watson, A. Williams
(The PLANET Collaboration)
Preprint no. 285
Accepted for publication in the Astrophysical Journal, 522, 1022.
Abstract
We present a method to analyze binary-lens microlensing light curves
with
one well-sampled fold caustic crossing. In general, the surface of
chi2 shows extremely complicated behavior over the 9-parameter space
that
characterizes binary lenses. This makes it difficult to systematically
search the space and verify that a given local minimum is a global
minimum. We show that for events with well-monitored caustics, the
caustic-crossing region can be isolated from the rest of the light curve
and easily fit to a 5-parameter function. Four of these
caustic-crossing
parameters can then be used to constrain the search in the larger
9-parameter space. This allows a systematic search for all solutions and
thus identification of all local minima. We illustrate this technique
using the PLANET data for MACHO 98-SMC-1, an excellent and publicly
available caustic-crossing data set. We show that a very broad range of
parameter combinations are compatible with the PLANET data set,
demonstrating that observations of binary-lens lightcurves with sampling
of only one caustic crossing do not yield unique solutions. The
corollary
to this is that the time of the second caustic crossing cannot be
reliably
predicted on the basis of early data including the first caustic
crossing
alone. We investigate the requirements for determination of a unique
solution and find that occasional observations of the first caustic
crossing may be sufficient to derive a complete solution.
Detection of Warm and Cold Phases of the Neutral ISM in a Damped
Ly-alpha Absorber
W.M. Lane, F.H. Briggs, and A. Smette
Preprint no. 284
Accepted for publication in the Astrophysical Journal, 2000
Abstract
We present a detailed study of the HI 21cm absorption system at
z=0.0912 towards the radio quasar B0738+313. The uncommonly narrow
main absorption line and weak secondary line are resolved for the
first time. In addition we find it necessary to add a third, broader
shallow component to obtain a good fit to the spectrum. Although the
harmonic mean spin temperature calculated by comparison of the 21cm
lines to the damped Ly-alpha line is Ts = 775 K, the thermal kinetic
temperatures of the two narrow components, calculated from their
widths, are much lower: Tk < 297 and < 103 K respectively. This
is the first case of a redshifted absorption system for which Tk is
measured to be less than Ts. We discuss this result in the context of
a two phase gas model, in which the damped Ly-alpha gas is sensitive
to a significant neutral column density of warm phase gas as well as
the cold phase gas of the narrow 21cm lines. The third component is
interpreted as representing the warm phase gas with with Tk <5050
K. The combined column density of the three 21cm components is
approximately equal to that derived from fits to the damped Ly-alpha
line.
ISO-SWS observations of interstellar solid 13CO2: heated ice
and the Galactic 12C/13C abundance ratio
A.C.A. Boogert, P. Ehrenfreund, P.A. Gerakines, A.G.G.M. Tielens,
D.C.B. Whittet, W.A. Schutte, E.F. van Dishoeck,
Th. de Graauw, L. Decin, T. Prusti
Preprint no. 283
Accepted for publication in Astronomy and Astrophysics
Abstract
We present observations of the stretching mode of 13CO2 ice along 13
lines of sight in the Galaxy, using the Short Wavelength Spectrometer
on board of the Infrared Space Observatory (ISO-SWS). Remarkable
variations are seen in the absorption band profile in the different
lines of sight. The main feature is attributed to 13CO2 mixed with
polar molecules such as H2O, and CH3OH. The high-mass protostars GL
2136, GL 2591, S 140 : IRS1, and W 3 : IRS5 show an additional narrow
substructure at 2282 cm-1 (4.382 um), which we attribute to a polar,
CH3OH-containing CO2 ice, that experienced heating. This heating
effect is sustained by a good correlation of the strength of the
substructure with dust and CO gas temperatures along the line of
sight, and anti-correlation with ice abundances. Thus, our main
conclusion is that interstellar CO2 ices around luminous protostars
are subjected to, and altered by, thermal processing and that it may
reflect the evolutionary stage of the nearby protostar. In contrast,
the ices around low mass protostars and in a quiescent cloud in our
sample do not show signs of thermal processing.
Furthermore, we determine for the first time the Galactic 12C/13C
ratio from the solid state as a function of Galacto-centric radius.
The 12CO2/13CO2 ratio for the local ISM (69+/-15), as well as the
dependence on Galacto-centric radius, are in good agreement with gas
phase (C18O, H2CO) studies. For the few individual objects for which
gas phase values are available, the 12C/13C ratios derived from CO2
tend to be higher compared to CO studies (albeit with 2.5 sigma
significance only). We discuss the implications of this possible
difference for the chemical origin of interstellar CO2.
The Planetary Nebulae Spectrograph
M. Arnaboldi, M. Capaccioli, N. Douglas, K. Kuijken, K. Freeman,
T. Axelrod, K. Taylor, R. Gilmozzi and R. Kudritzki
Preprint no. 282
To be published in the Proceedings of the SAIT* symposium,
Naples 1999
*Societa Astronomica Italiana
Abstract
We present the Planetary Nebulae Spectrograph project. This is an
international collaboration aimed at building a dedicated slitless
spectrograph for the detection of extragalactic planetary nebulae to be
mounted at the 4 metre WHT and TNG. The scientific projects and the
scope of such an instrument are outlined. The feasibility studies and
the final optical design are presented.
Neutral hydrogen and dark matter in spiral galaxies
Renzo Sancisi
Preprint no. 281
Figures 1 and 2 are separated from the text
figure 1,
figure 2.
To be published in: "Toward a New Millennium in Galaxy Morphology"
(eds. D.L. Block, I. Puerari, A. Stockton and D. Ferreira),
Conf. Proc., Kluwer, Dordrecht.
Abstract
The first part presents a brief review of the main HI properties
of isolated, normal spiral galaxies and of the phenomena which seem
to characterize and dominate their internal metabolism.
In the second part attention is drawn to all those processes, such
as tidal interactions, accretion and mergers, that depend
on the galaxy environment and may play a
significant role in galaxy formation and evolution.
In the third part the observational evidence for the dark matter
component of spiral galaxies is discussed.
On the axis ratio of the stellar velocity ellipsoid in disks
of spiral galaxies
P.C. van der Kruit and
R. de Grijs
Preprint no. 280
Accepted for publication in: Astronomy and Astrophysics.
Abstract
The spatial distribution of stars in a disk of a galaxy can be described
by a radial scalelength and a vertical scaleheight. The ratio of these
two scale parameters contains information on the axis ratio of the
velocity ellipsoid, i.e. the ratio of the vertical to radial stellar
velocity dispersions of the stars, at least at some fiducial distance
from the center. The radial velocity dispersion correlates well with
the amplitude of the rotation curve and with the disk integrated
magnitude, as was found by Bottema (1993). These relations can
be understood as the result of the stellar disk being (marginally)
stable against local instabilities at all length scales. This is
expressed by Toomre's well-known criterion, which relates the sheer in
the rotation to a minimum value that the radial stellar velocity
dispersion should have for stability for a given surface density. Via
the Tully-Fisher (1977) relation, the velocity dispersion then becomes
related
to the integrated magnitude and hence to the scalelength. The vertical
velocity dispersion relates directly to the scaleheight through
hydrostatic equilibrium. It can be shown that the ratio of the two
length scales relates to the axis ratio of the velocity ellipsoid only
through the Toomre parameter Q and in particular does not require
a
choice of the mass-to-light ratio or a distance scale.
We have applied this to the statistically complete sample of edge-on
galaxies, for which de Grijs (1997) has performed surface photometry and
has
determined the length scales in the stellar light distribution.
Properties of the Stellar Velocity Ellipsoid and Stability in
Disks of Spiral Galaxies
P.C. van der Kruit
Preprint no. 279
To be published in: "Toward
a New Millenium in Galaxy Morphology",
Conf. Proc. (Johannesburg, South Africa, September 1999).
Abstract
Disks of spiral galaxies are characterized by effectively exponential
brightness and presumably density distributions in both the radial
and vertical directions. It is to be expected that the ratio
between the scalelength and -height bears a relation
to the axis ratio of the stellar velocity ellipsiod. Hydrostatic
equilibrium connects the vertical velocity dispersion to the
scaleheight.
In the radial direction the velocity dispersion relates to the
scalelength
through conditions of local stability. Preliminary applications are
presented.
The Milky Way compared to external galaxies
P.C. van der Kruit
Preprint No. 278
To be published in: "The Legacy of J.C. Kapteyn",
Conf. Proc. (Groningen, the Netherlands, June 1999).
Abstract
Kapteyn's work to map the Sidereal System was based on star counts. Now
that we know that the stellar system is comparable to many external
spiral galaxies, this information can be used to further constrain
models for the structure of our Galaxy. It is now possible
to also use surface brightness distributions, both in the optical from
the Pioneer spacecrafts and in the near-infrared with the COBE/DIRBE
experiment. Star counts and surface photometry are discussed in a
comparative sense. It turns out, that at least away from directions
close to the Galactic center, surface brightness is dominated by the
contribution from the disk, while faint star counts are dominated by the
halo population. If low Galactic latitudes are ignored,
surface brightness data can be used to constrain the parameters of
the old stellar disk.
I repeat an earlier discussion in which older star counts are compared
with current models for the distribution of stars in the Galactic disk.
Herschel, in his
famous "Star Gauges" of 1785,
counted stars rather consistently to a visual magnitude
of 14.5 to 15. This is consistent with Herschel's
own values for the "gage or space penetrating powers" of his
telescopes and his "extent
of telescopic vision". Counts early this century by Kapteyn and van
Rhijn
seem to have significantly incorrect magnitude scales compared to the
prediction of models, in the sense of being too bright by half a
magnitude or more at photograpic magnitude 18.5. Yet, the counts are
consistent
across the sky and with limits on current parameters for the
Galactic disk.
A discussion is given of the value of the exponential scalelength of
the Galactic disk. A value of 4.5 to 5.0 kpc is still preferred in spite
of smaller values from surveys in the near-infrared. Finally, I show
that as far as structural parameters are concerned, NGC 891, 5033 and
5375 closely resemble the Milky Way Galaxy.
The binary gravitational lens and its extreme cases
M. Dominik
Preprint No. 277
Accepted for publication in:
Astronomy and Astrophysics, 349, 108, 1999.
Abstract
The transition of the binary gravitational lens from the equal mass case
to small (planetary) mass ratios q is studied. It is shown how the limit
of a (pure shear) Chang-Refsdal lens is approached, under what
conditions
the Chang-Refsdal approximation is valid, and how the 3 different
topologies of the critical curves and caustics for a binary lens are
mapped onto the 2 different topologies for a Chang-Refsdal lens with
pure
shear. It is shown that for wide binaries, the lensing in the vicinity
of
both lens objects can be described by a Taylor-expansion of the
deflection
term due to the other object, where the Chang-Refsdal approximation
corresponds to a truncation of this series. For close binaries, only the
vicinity of the secondary, less massive, object can be described in this
way. However, for image distances much larger than the separation of the
lens objects, any binary lens can be approximated by means of multipole
expansion, where the first non-trivial term is the quadrupole term. It
is
shown that an ambiguity exists between wide and close binary lenses,
where
the shear at one of the objects due to the other object for the wide
binary is equal to the absolute value of the eigenvalues of the
quadrupole
moment for the close binary. This analysis provides the basis for a
classification of binary lens microlensing events, especially of
planetary
events, and an understanding of present ambiguities.
Lensed galaxies in Abell 370. II. The ultraviolet properties
of arclets and the star formation rate at high redshift
J. Bezecourt, G. Soucail, R.S. Ellis, J.-P. Kneib
Preprint No. 276
Accepted for publication in:
Astronomy and Astrophysics.
Abstract
We discuss the statistical properties of faint background galaxies
detected in a deep Hubble Space Telescope ultraviolet (F336W) Wide
Field Planetary Camera 2 image of the lensing cluster Abell 370
(z=0.37). By combining modelled field galaxy counts at this
wavelength with a detailed mass model for the cluster, we develop
techniques for predicting the expected redshift distribution of
lensed sources and find the bulk of the sources should be
moderately magnified sources whose redshifts lie between 0.5 and
2. We compare these predictions with redshift estimates derived
from the lens inversion method which utilises the shapes of
individual arclets in the context of a known field ellipticity
distribution. This allows us to infer the comoving star formation
rate for the range 0.5<z<2 where there is currently little
spectroscopic data. We discuss our results in the context of
contemporary pictures for the history of star formation.
Lensed galaxies in Abell 370. I. Modeling the number counts and
redshift distribution of background sources
J. Bezecourt, J.P. Kneib, G. Soucail, T.M.D. Ebbels
Preprint No. 275
Accepted for publication in:
Astronomy and Astrophysics.
Abstract
We present new observations of the cluster-lens Abell 370: a deep
HST/WFPC2 F675W image and ESO 3.6m spectroscopy of faint galaxies.
These observations shed new light on the statistical properties of
faint lensed galaxies. In particular, we spectroscopically confirm
HST/WFPC2 F675W image and ESO 3.6m spectroscopy of faint galaxies.
These observations shed new light on the statistical properties of
faint lensed galaxies. In particular, we spectroscopically confirm
the multiple image nature of the B2-B3 gravitational pair
(Kneib et al. 1993), and determine a redshift of z=0.806±0.002 which
is in very good agreement with earlier predictions. A refined mass
model of the cluster core (that includes cluster galaxy halos) is
presented, based on a number of newly identified multiple
images. Following Bezecourt et al. (1998a), we combine the new cluster
mass
model with a spectrophotometric prescription for galaxy evolution to
predict the arclets number counts and redshift distribution in the HST
image. In particular, the ellipticity distribution of background
sources is taken into account, in order to properly estimate the
statistical number and redshift distribution of arclets. We show that
the redshift distribution of arclets, and particularly its
high redshift tail can be used as a strong constraint to disentangle
different galaxy evolution scenarios. A hierarchical model which
includes number density evolution is favored by our
analysis. Finally, we compute the depletion curves for the faint
galaxy number counts and discuss their wavelength dependence.
Surface photometry of bulge dominated low surface brightness
galaxies
M. Beijersbergen, W.G.J. de Blok, and J.M. van der Hulst
Preprint No. 274
Accepted for publication in:
Astronomy and Astrophysics.
Abstract
We present results of broad band BVRI observations of a sample of
galaxies with a low surface brightness (LSB) disk and a bulge. These
galaxies are well
described as exponential disks and exponential bulges with no
preferred value for either scale length or central surface
brightness. The median B band disk scale length is
12.6 kpc (H0 = 75 km/s/Mpc)
which is much larger than scale lengths of typical (disk dominated) LSB
or high
surface brightness (HSB) galaxies. Furthermore, the disk and bulge
scale lengths are correlated, suggesting a coupling in the formation.
Bulge dominated LSB galaxies are observed to be redder than
disk dominated LSB galaxies and
their bulge-to-disk ratios are increasing towards redder
wavelengths. We find colors that are comparable to or bluer than HSB
galaxies
of the same morphological types. Bulge dominated LSB galaxies are
therefore not
faded
HSB galaxies with no current star formation. We find that bulge
dominated LSB galaxies fit in with
the general trends defined by the HSB galaxies.
The properties of these bulge dominated LSB galaxies show that LSB
galaxies do not just come in two varieties. They cover the entire
range in optical and morphological properties between late-type disk
dominated LSBs and giant Malin-1-like LSBs. LSB galaxies thus also
form a LSB Hubble sequence, parallel to the classical HSB one.
Spectrophotometry of nearby field galaxies: the data
R.A. Jansen, D. Fabricant, M. Franx, N. Caldwell
Preprint No. 273
Accepted for publication in:
Astrophysical Journal Suppl. (Vol. 127, March 2000)
Abstract
We have obtained integrated and nuclear spectra, as well as U, B, R
surface
photometry, for a representative sample of 196 nearby galaxies. These
galaxies
span the entire Hubble sequence in morphological type, as well as a wide
range
of luminosities (M_B=-14 to -22). Here we present the spectrophotometry
for
these galaxies. The selection of the sample and the U, B, R surface
photometry
is described in a companion paper (Paper I). Our goals for the project
include
measuring the current star formation rates and metallicities of these
galaxies,
and elucidating their star formation histories, as a function of
luminosity and
morphology. We thereby extend the work of Kennicutt (1992a) to lower
luminosity
systems. We anticipate that our study will be useful as a benchmark for
studies
of galaxies at high redshift.
We describe the observing, data reduction and calibration techniques,
and
demonstrate that our spectrophotometry agrees well with that of
Kennicutt. The
spectra span the range 3550--7250 A at a resolution (FWHM) of ~6 A, and
have an
overall relative spectrophotometric accuracy of +/- 6 per cent. We
present a
spectrophotometric atlas of integrated and nuclear rest-frame spectra,
as well
as tables of equivalent widths and synthetic colors.
We study the correlations of galaxy properties determined from the
spectra
and images. Our findings include: (1) galaxies of a given morphological
class
display a wide range of continuum shapes and emission line strengths if
a broad
range of luminosities are considered, (2) emission line strengths tend
to in-
crease and continua tend to get bluer as the luminosity decreases, and
(3) the
scatter on the general correlation between nuclear and integrated
H_alpha
emission line strengths is large.
Surface photometry of nearby field galaxies: the data
R.A. Jansen, M. Franx, D. Fabricant, N. Caldwell
Preprint No. 272
Accepted for publication in:
Astrophysical Journal Suppl. (Vol. 127, March 2000)
Abstract
We have obtained integrated spectra and multi-filter photometry for a
repre-
sentative sample of ~200 nearby galaxies. These galaxies span the entire
Hubble
sequence in morphological type, as well as a wide range of luminosities
(M_B =
-14 to -22) and colors (B-R=0.4 to 1.8). Here we describe the sample
selection
criteria and the U, B, R surface photometry for these galaxies. The
spectro-
photometric results will be presented in a companion paper. Our goals
for the
project include measuring the current star formation rates and
metallicity of
these galaxies, and elucidating their star formation histories, as a
function
of luminosity and morphology. We thereby extend the work of Kennicutt
(1992) to
lower luminosity systems. We anticipate that our study will be useful as
a
benchmark for studies of galaxies at high redshift.
We discuss the observing, data reduction and calibration techniques,
and show
that our photometry agrees well with previous work in those cases where
earlier
data are available. We present an atlas of images, radial surface
brightness
profiles and color profiles, as well as tables of derived parameters.
The atlas
and tables of measurements will be made available electronically.
We study the correlations of galaxy properties determined from the
galaxy
images. Our findings include: (1) colors determined within the effective
radius
correlate better with morphological type than with M_B and (2) 50 per
cent of
the low luminosity galaxies are bluest in their centers.
Planetary Microlensing: Present Status and Long-term Goals
Penny D. Sackett
Preprint No. 271
To appear in the Springer-Verlag series "ESO Astrophysics Symposia".
Invited Review at VLT Opening Symposium, Antofagasta, Chile, March 1999.
Abstract
Massive gravitational microlensing programs were begun about a decade
ago as
a means to search for compact baryonic dark matter in the Galaxy, but
before
the first events were detected the technique was also proposed as a
means of
detecting extra-solar planets in our Galaxy. Current microlensing planet
searches, which have been underway for four years, are sensitive to
jovian-mass
planets orbiting a few to several AU from their parent Galactic stars.
Within
two years, sufficient data should be in hand to characterize or
meaningfully
constrain the frequency of massive planets in this range of parameter
space,
nicely complementing information about planets at smaller orbital radii
now
being provided by radial velocity searches. In principle, the technique
could
be pushed to smaller planetary masses, but only if a larger number of
faint
microlensed sources can be monitored with higher precision and temporal
sampling. The VST on Paranal, with spectroscopic follow-up with the VLT,
may be
the ideal instrument for such an ambitious program.
Galaxy kinematics from counter-dispersed imaging
N.G. Douglas, K. Taylor
Preprint No. 270
Accepted for publication in:
Monthly Notices of the Royal Astronomical Society.
Abstract
Determining the internal kinematics of a galaxy from planetary nebulae
(PN) is usually a two-step process in which the candidate PN are first
identified in a target galaxy and then, in a follow up run, spectra are
obtained. We have implemented a new technique in which two dispersed
images at the wavelength of the [OIII] emission line at 5007 Å are
combined to yield positions, magnitudes and velocities of the PN
population in a single step. A reduction in observing time of about a
factor 2 is attainable. We present here the proof-of-principle results.
The kinematics of the bulge and the disc of NGC 7331
Roelof Bottema
Preprint No. 269
Accepted for publication in:
Astronomy & Astrophysics, Main Journal
Abstract
Results are presented of spectroscopic emission and absorption line
observations along the major axis of the Sb galaxy NGC 7331. The
kinematics of the ionized gas and stellar component are derived, being
regular and symmetric with respect to the centre of the galaxy.
Contrary to what may be expected, for radii less than 40 arcsec
the emission line gas appears to rotate slower than the stars.
A likely explanation for this phenomenon is an inclined and warped gas
layer
in those inner regions. In the bulge dominated region the absorption
line profiles are asymmetric in the sense that they have a shallow
extension towards the systemic velocity. No counterrotating stellar
component is observed, which is contrary to previous
claims. As demonstrated, these claims might be based on a wrong
interpretation of the employed analysis method.
Outside the bulge dominated region the stellar radial velocities
are in agreement with the neutral hydrogen dynamics and the stellar
velocity dispersion decreases towards larger radii.
A detailed bulge/disc light decomposition has been made.
This has been used to construct a kinematical model of NGC 7331
from which model absorption line profiles were calculated. These
profiles have been compared with the observations and model parameters
have been adjusted to obtain a good match. It appeared necessary to
combine a rapidly rotating disc having a radially
decreasing velocity dispersion with a slowly rotating
constant dispersion bulge. Then, simultaneously, the observed stellar
radial velocities, the velocity dispersions and the observed asymmetry
of the line profile could be explained satisfactorily. An even better
fit
to the data can be achieved when the disc is relatively
thinner and colder inside the bulge region.
For the disc the stellar velocity dispersions and photometry
result in a mass-to-light ratio of 1.6±0.7 in the I-band.
This value agrees with previous determinations for other discs
using observed velocity dispersions. A rotation curve analysis
allows the calculation of the mass-to-light ratio of the bulge
which amounts to 6.8 in the I-band; considerably larger than the
disc value. It appears that the mass distribution of NGC 7331
is completely dominated by the combination of bulge
and dark halo at all radii. Comparing well determined mass-to-light
ratios of a number of bulges with disc values the mass-to-light
ratio of the bulge is, on average, three times as large as
the mass-to-light ratio of the disc in the I-band.
For the B-band this ratio goes up to 7.2, a fact which
should have cosmological consequences.
Limb-Darkening of a K Giant in the Galactic Bulge:
PLANET Photometry of MACHO 97-BLG-28
M.D. Albrow, J.-P. Beaulieu, J.A.R. Caldwell, M. Dominik,
J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies,
R.M. Naber, J.-W. Pel, K. Pollard, P.D. Sackett, K.C. Sahu,
P. Vermaak, R. Watson, A. Williams (The PLANET Collaboration),
and M. S. Sahu
Preprint No. 268
Accepted for publication in:
volume 522 of the 1999 Astrophysical Journal
Abstract
We present the PLANET photometric dataset for the binary-lens
microlensing
event MACHO 97-BLG-28 consisting of 696 I and V-band measurements,
and analyze it to determine the radial surface brightness profile
of the Galactic bulge source star. The microlensed source, demonstrated
to be a
K giant by our independent spectroscopy, crossed the central isolated
cusp of the lensing binary, generating a sharp peak in the light curve
that was well-resolved by dense (3 - 30 minute) and continuous
monitoring
from PLANET sites in Chile, South Africa, and Australia. Our modeling of
these data has produced stellar profiles for the source star in the
I and V bands that are in excellent agreement with those predicted by
stellar atmospheric models for K giants. The limb-darkening coefficients
presented here are the first derived from microlensing, among the first
for normal giants by any technique, and the first for any star as
distant
as the Galactic bulge. Modeling indicates that the lensing binary
has a mass ratio q = 0.23 and an (instantaneous) separation in units of
the
angular Einstein ring radius of d = 0.69. For a lens in the Galactic
bulge,
this corresponds to a typical stellar binary with a projected separation
between 1 and 2 AU. If the lens lies closer, the separation is smaller,
and one or both of the lens objects is in the brown dwarf regime.
Assuming that the source is a bulge K2 giant at 8 kpc, the relative
lens-source proper motion is mu = 19.4 +/- 2.6 km/s kpc, consistent
with a disk or bulge lens. If the non-lensed blended light is due to
a single star, it is likely to be a young white dwarf in the bulge,
consistent with the blended light coming from the lens itself.
The Shape of Dark Matter Halo
Penny D. Sackett
Preprint No. 267
Invited Review to appear in "Galaxy Dynamics" (eds. D. Merritt,
J.A. Sellwood and M. Valluri), proceedings of the
Rutgers Conferece, A.S.P. Conf. Series, 1999
Abstract
Techniques for inferring the radial and geometric form of dark matter
halos and the results they have produced to date are reviewed.
Dark halos appear to extend to at least ~50 kpc with total enclosed
masses that rise linearly with radius R. Whether this behavior
can be extrapolated to distances as large as 200 kpc and beyond
is controversial; results at this radius are model-dependent.
Observationally, the geometrical form of the dark halo can be
characterized by the equatorial axis ratio b/a (ovalness) and
vertical-to-equatorial axis ratio c/a (flattening) of the total density.
Different techniques consistently yield b/a 0.7 (and thus
b/a 0.9 for the potential) at R~20 kpc, with more axisymmetric values,
b/a >~ 0.8, being more likely. Results are less consistent for the
vertical flattening, perhaps due to the difference in the spatial
regions
probed by different techniques or inappropriate assumptions.
Techniques that probe furthest from the stellar plane z~15 kpc
consistently implicate substantially flattened c/a = 0.5 +/- 0.2 dark
halos.
These axis ratios are in acceptable agreement with expectations
from N-body simulations of cold dark matter mixed with ~10%
dissipational gas.