1,257 research outputs found
Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
We present a direct method for isolating the component of the starlight
blocked by a planet as it transits its host star, and apply it to spectra of
the bright transiting planet HD 189733b. We model the global shape of the
stellar cross-correlation function as the convolution of a limb-darkened
rotation profile and a gaussian representing the Doppler core of the average
photospheric line profile. The light blocked by the planet during the transit
is a gaussian of the same intrinsic width, whose trajectory across the line
profile yields a precise measure of the misalignment angle and an independent
measure of v sin I. We show that even when v sin I is less than the width of
the intrinsic line profile, the travelling Doppler "shadow" cast by the planet
creates an identifiable distortion in the line profiles which is amenable to
direct modelling. Direct measurement of the trajectory of the missing starlight
yields self-consistent measures of the projected stellar rotation rate, the
intrinsic width of the mean local photospheric line profile, the projected
spin-orbit misalignment angle, and the system's centre-of-mass velocity.
Combined with the photometric rotation period, the results give a geometrical
measure of the stellar radius which agrees closely with values obtained from
high-precision transit photometry if a small amount of differential rotation is
present in the stellar photosphere.Comment: 8 pages, 5 figures, 2 tables; accepted by MNRA
Twenty-One New Light Curves of OGLE-TR-56b: New System Parameters and Limits on Timing Variations
Although OGLE-TR-56b was the second transiting exoplanet discovered, only one
light curve, observed in 2006, has been published besides the discovery data.
We present twenty-one light curves of nineteen different transits observed
between July 2003 and July 2009 with the Magellan Telescopes and Gemini South.
The combined analysis of the new light curves confirms a slightly inflated
planetary radius relative to model predictions, with R_p = 1.378 +/- 0.090 R_J.
However, the values found for the transit duration, semimajor axis, and
inclination values differ significantly from the previous result, likely due to
systematic errors. The new semimajor axis and inclination, a = 0.01942 +/-
0.00015 AU and i = 73.72 +/- 0.18 degrees, are smaller than previously
reported, while the total duration, T_14 = 7931 +/- 38 s, is 18 minutes longer.
The transit midtimes have errors from 23 s to several minutes, and no evidence
is seen for transit midtime or duration variations. Similarly, no change is
seen in the orbital period, implying a nominal stellar tidal decay factor of
Q_* = 10^7, with a three-sigma lower limit of 10^5.7.Comment: 14 pages, 5 figures, accepted to Ap
VARIATIONS IN THE RESPONSES OF C57BL/10J AND A/J MICE TO SHEEP RED BLOOD CELLS : I. SEROLOGICAL CHARACTERIZATION AND GENETIC ANALYSIS
In response to repeated injections of sheep red blood cells, C57BL/10J mice produce predominantly 19S antibody in increasingly higher amounts, while A/J mice initially produce 19S antibody and then switch to produce increasing 7S antibody titers. In an F1 generation all mice responded like the C57BL/10J mice. Backcross data implied genetic control involving at least three loci
Five New Transits of the Super-Neptune HD 149026
We present new photometry of HD 149026 spanning five transits of its
"super-Neptune" planet. In combination with previous data, we improve upon the
determination of the planet-to-star radius ratio: R_p/R_star =
0.0491^{+0.0018}_{-0.0005}. We find the planetary radius to be 0.71 +/- 0.05
R_Jup, in accordance with previous theoretical models invoking a high metal
abundance for the planet. The limiting error is the uncertainty in the stellar
radius. Although we find agreement among four different ways of estimating the
stellar radius, the uncertainty remains at 7%. We also present a refined
transit ephemeris and a constraint on the orbital eccentricity and argument of
pericenter, e cos(omega) = -0.0014 +/- 0.0012, based on the measured interval
between primary and secondary transits.Comment: To appear in ApJ [19 pages
The Transit Light Curve Project. X. A Christmas Transit of HD 17156b
Photometry is presented of the Dec. 25, 2007 transit of HD 17156b, which has
the longest orbital period and highest orbital eccentricity of all the known
transiting exoplanets. New measurements of the stellar radial velocity are also
presented. All the data are combined and integrated with stellar-evolutionary
modeling to derive refined system parameters. The planet's mass and radius are
found to be 3.212_{-0.082}^{+0.069} Jupiter masses and 1.023_{-0.055}^{+0.070}
Jupiter radii. The corresponding stellar properties are 1.263_{-0.047}^{+0.035}
solar masses and 1.446_{-0.067}^{+0.099} solar radii. The planet is smaller by
1 sigma than a theoretical solar-composition gas giant with the same mass and
equilibrium temperature, a possible indication of heavy-element enrichment. The
midtransit time is measured to within 1 min, and shows no deviation from a
linear ephemeris (and therefore no evidence for orbital perturbations from
other planets). We provide ephemerides for future transits and superior
conjunctions. There is an 18% chance that the orbital plane is oriented close
enough to edge-on for secondary eclipses to occur at superior conjunction.
Observations of secondary eclipses would reveal the thermal emission spectrum
of a planet that experiences unusually large tidal heating and insolation
variations.Comment: To appear in ApJ [26 pages
DEPRESSION BY ANTIBODY OF THE IMMUNE RESPONSE TO HOMOGRAFTS AND ITS ROLE IN IMMUNOLOGICAL ENHANCEMENT
This paper reports tests of two hypotheses that have been proposed to account for the enhanced growth of tumor homografts in the presence of antiserum reactive with the graft (immunological enhancement). According to the first hypothesis, enhancement is due to some "physiological" alteration in the tumor, induced by its contact with antiserum, which insures its survival despite the hostile response of the host. According to the second hypothesis, antiserum alters the response of the host. By blocking the development of the cellular type of immunity, which is the main agent in graft destruction, it permits the graft to survive. To test hypothesis 1, strain A tumor SaI was passed from A's, and from enhanced B10.D2's, into untreated B10.D2's. The per cent of deaths was essentially the same in both groups (48 and 44 per cent, respectively); there was no evidence that passage through enhanced B10.D2's altered the capacity of the tumor to grow in the foreign strain. Several other groups of mice included in the experiment all confirmed this conclusion. The experiment failed to confirm hypothesis 1. In the tests of hypothesis 2, the effect of isoantiserum on immune responses of both the humoral and cellular type was measured. When antiserum was given together with foreign strain lymphoid cells (antigen), almost no additional antibody was manufactured; in contrast with this, controls receiving foreign cells only produced red cell agglutinating antibody in high titer. The effect of antiserum on the development of immunity of the cellular type was tested by the method of Winn. In this assay, presumptively immune node cells, in various dilutions, are mixed with tumor cells and injected into appropriate mice. Immunity is indicated by inhibited tumor growth. Antiserum given at the same time as a tumor homograft greatly depressed the immunity of the cells expressed from the draining nodes. At 6 days after the graft, the level of immunity of cells from treated mice was 1/24th to 1/32nd that of cells from controls receiving tumor alone. The same sort of depressing effect was noted when the immunizing tissue was foreign thymus or embryo. Antiserum given 1 or more days after the immunizing tissue also resulted in a lower level of cellular immunity (but the assay used in this case was a less critical one). These results provide an adequate explanation of the phenomenon of immunological enhancement, at least as it occurs in the particular test system used in these experiments. Since it is cellular immunity rather than humoral antibody that inhibits the growth of most grafts (transplantable leukemias are an exception), the depression of this immunity by antibody is favorable to the growth of a homograft
The Rotation Period of the Planet-Hosting Star HD 189733
We present synoptic optical photometry of HD 189733, the chromospherically
active parent star of one of the most intensively studied exoplanets. We have
significantly extended the timespan of our previously reported observations and
refined the estimate of the stellar rotation period by more than an order of
magnitude: days. We derive a lower limit on the
inclination of the stellar rotation axis of 56\arcdeg (with 95% confidence),
corroborating earlier evidence that the stellar spin axis and planetary orbital
axis are well aligned.Comment: To appear in A
The Transit Light Curve Project. V. System Parameters and Stellar Rotation Period of HD 189733
We present photometry of HD 189733 during eight transits of its close-in
giant planet, and out-of-transit photometry spanning two years. Using the
transit photometry, we determine the stellar and planetary radii and the
photometric ephemeris. Outside of transits, there are quasiperiodic flux
variations with a 13.4 day period that we attribute to stellar rotation. In
combination with previous results, we derive upper limits on the orbital
eccentricity, and on the true angle between the stellar rotation axis and
planetary orbit (as opposed to the angle between the projections of those axes
on the sky).Comment: Accepted for publication in AJ [21 pages]; minor change
Non-Detection of Polarized, Scattered Light from the HD 189733b Hot Jupiter
Using the POLISH instrument, I am unable to reproduce the large-amplitude
polarimetric observations of Berdyugina et al. (2008) to the >99.99% confidence
level. I observe no significant polarimetric variability in the HD 189733
system, and the upper limit to variability from the exoplanet is Delta_P < 7.9
x 10^(-5) with 99% confidence in the 400 nm to 675 nm wavelength range.
Berdyugina et al. (2008) report polarized, scattered light from the atmosphere
of the HD 189733b hot Jupiter with an amplitude of two parts in 10^4. Such a
large amplitude is over an order of magnitude larger than expected given a
geometric albedo similar to other hot Jupiters. However, my non-detection of
polarimetric variability phase-locked to the orbital period of the exoplanet,
and the lack of any significant variability, shows that the polarimetric
modulation reported by Berdyugina et al. (2008) cannot be due to the exoplanet.Comment: 24 pages, 8 figures, accepted for publication in Ap
A High Eccentricity Component in the Double Planet System Around HD 163607 and a Planet Around HD 164509
We report the detection of three new exoplanets from Keck Observatory. HD
163607 is a metal-rich G5IV star with two planets. The inner planet has an
observed orbital period of 75.29 0.02 days, a semi-amplitude of 51.1
1.4 \ms, an eccentricity of 0.73 0.02 and a derived minimum mass of
\msini = 0.77 0.02 \mjup. This is the largest eccentricity of any known
planet in a multi-planet system. The argument of periastron passage is 78.7
2.0; consequently, the planet's closest approach to its parent
star is very near the line of sight, leading to a relatively high transit
probability of 8%. The outer planet has an orbital period of 3.60 0.02
years, an orbital eccentricity of 0.12 0.06 and a semi-amplitude of 40.4
1.3 \ms. The minimum mass is \msini = 2.29 0.16 \mjup. HD 164509 is
a metal-rich G5V star with a planet in an orbital period of 282.4 3.8
days and an eccentricity of 0.26 0.14. The semi-amplitude of 14.2
2.7 \ms\ implies a minimum mass of 0.48 0.09 \mjup. The radial velocities
of HD 164509 also exhibit a residual linear trend of -5.1 0.7 \ms\ per
year, indicating the presence of an additional longer period companion in the
system. Photometric observations demonstrate that HD 163607 and HD 164509 are
constant in brightness to sub-millimag levels on their radial velocity periods.
This provides strong support for planetary reflex motion as the cause of the
radial velocity variations.Comment: 10 pages, 8 figures, accepted to Ap
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