* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Stars/galaxy News -> HD189733
Post Info
TOPIC: HD189733
Blobrana


L

Posts: 131433
Date:
RE: HD189733
Permalink  
 

Title: A Ground-Based Albedo Upper Limit for HD 189733b from Polarimetry
Author: Sloane J. Wiktorowicz (1), Larissa A. Nofi (1 and 2), Daniel Jontof-Hutter (3 and 4), Pushkar Kopparla (5), Gregory P. Laughlin (1), Ninos Hermis (1), Yuk L. Yung (5), Mark R. Swain (6) ((1) UC Santa Cruz, (2) Institute for Astronomy, (3) NASA Ames Research Center, (4) Penn State, (5) Caltech, (6) JPL)

We present 50 nights of polarimetric observations of HD 189733 in B band using the POLISH2 aperture-integrated polarimeter at the Lick Observatory Shane 3-m telescope. This instrument, commissioned in 2011, is designed to search for Rayleigh scattering from short-period exoplanets due to the polarised nature of scattered light. Since these planets are spatially unresolvable from their host stars, the relative contribution of the planet-to-total system polarisation is expected to vary with an amplitude of order 10 parts per million (ppm) over the course of the orbit. Non-zero and also variable at the 10 ppm level, the inherent polarisation of the Lick 3-m telescope limits the accuracy of our measurements and currently inhibits conclusive detection of scattered light from this exoplanet. However, the amplitude of observed variability conservatively sets a 3 sigma upper limit to the planet-induced polarisation of the system of 58 ppm in B band, which is consistent with a previous upper limit from the POLISH instrument at the Palomar Observatory 5-m telescope (Wiktorowicz 2009). A physically-motivated Rayleigh scattering model, which includes the depolarising effects of multiple scattering, is used to conservatively set a 3 sigma upper limit to the geometric albedo of HD 189733b of A_g < 0.37. This value is consistent with the value Ag=0.226±0.091 derived from occultation observations with HST STIS (Evans et al. 2013), but it is inconsistent with the large A_g=0.61±0.12 albedo reported by (Berdyugina et al. 2011).

Read more (785kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
HD 189733 b
Permalink  
 

Title: First exoplanet transit observation with the Stratospheric Observatory for Infrared Astronomy: Confirmation of Rayleigh scattering in HD 189733 b with HIPO
Author: Daniel Angerhausen, Georgi Mandushev, Avi Mandell, Edward W. Dunham, Eric E. Becklin, Peter L. Collins, Ryan T. Hamilton, Sarah E. Logsdon, Michael W. McElwain, Ian S. McLean, Enrico Pfueller, Maureen L. Savage, Sachindev S. Shenoy, William Vacca, Jeffry VanCleve, Juergen Wolf

Here we report on the first successful exoplanet transit observation with the Stratospheric Observatory for Infrared Astronomy (SOFIA). We observed a single transit of the hot Jupiter HD 189733 b, obtaining two simultaneous primary transit lightcurves in the B and z' bands as a demonstration of SOFIA's capability to perform absolute transit photometry. We present a detailed description of our data reduction, in particular the correlation of photometric systematics with various in-flight parameters unique to the airborne observing environment. The derived transit depths at B and z' wavelengths confirm a previously reported slope in the optical transmission spectrum of HD 189733 b. Our results give new insights to the current discussion about the source of this Rayleigh scattering in the upper atmosphere and the question of fixed limb darkening coefficients in fitting routines.

Read more (733kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
HD 189733b
Permalink  
 

Title: Modelling the local and global cloud formation on HD 189733b
Author: G. Lee, Ch. Helling, I. Dobbs-Dixon, D. Juncher

Context. Observations suggest that exoplanets such as HD 189733b form clouds in their atmospheres which have a strong feedback onto their thermodynamical and chemical structure, and overall appearance.
Aims. Inspired by mineral cloud modelling efforts for Brown Dwarf atmospheres, we present the first spatially varying kinetic cloud model structures for HD 189733b.
Methods. We apply a 2-model approach using results from a 3D global radiation-hydrodynamic simulation of the atmosphere as input for a detailed, kinetic cloud formation model. Sampling the 3D global atmosphere structure with 1D trajectories allows us to model the spatially varying cloud structure on HD 189733b. The resulting cloud properties enable the calculation of the scattering and absorption properties of the clouds.
Results. We present local and global cloud structure and property maps for HD 189733b. The calculated cloud properties show variations in composition, size and number density of cloud particles which are strongest between the dayside and nightside. Cloud particles are mainly composed of a mix of materials with silicates being the main component. Cloud properties, and hence the local gas composition, change dramatically where temperature inversions occur locally. The cloud opacity is dominated by absorption in the upper atmosphere and scattering at higher pressures in the model. The calculated 8µm single scattering Albedo of the cloud particles are consistent with Spitzer bright regions. The cloud particles scattering properties suggest that they would sparkle/reflect a midnight blue colour at optical wavelengths.

Read more (11628kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Updated Spitzer Emission Spectroscopy of Bright Transiting Hot Jupiter HD189733b
Author: Kamen O. Todorov, Drake Deming, Adam S. Burrows, Carl J. Grillmair

We analyse all existing secondary eclipse time series spectroscopy of hot Jupiter HD189733b acquired with the now defunct Spitzer/IRS instrument. We describe the novel approaches we develop to remove the systematic effects and extract accurate secondary eclipse depths as a function of wavelength in order to construct the emission spectrum of the exoplanet. We compare our results to a previous study by Grillmair et al. that did not examine all data sets available to us. We are able to confirm the detection of a water feature near 6µm claimed by Grillmair et al. We compare the planetary emission spectrum to three model families -- based on isothermal atmosphere, gray atmosphere, and two realisations of the complex radiative transfer model by Burrows et al., adopted in Grillmair et al.'s study. While we are able to reject the simple isothermal and gray models based on the data at the 97% level just from the IRS data, these rejections hinge on eclipses measured within relatively narrow wavelength range, between 5.5 and 7µm. This underscores the need for observational studies with broad wavelength coverage and high spectral resolution, in order to obtain robust information on exoplanet atmospheres.

Read more (852kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
RE: HD189733
Permalink  
 

Title: A new look at Spitzer primary transit observations of the exoplanet HD189733b
Author: Giuseppe Morello, Ingo P. Waldmann, Giovanna Tinetti, Giovanni Peres, Giuseppina Micela, Ian D. Howarth

Blind source separation techniques are used to reanalyse two exoplanetary transit lightcurves of the exoplanet HD189733b recorded with the IR camera IRAC on board the Spitzer Space Telescope at 3.6m during the "cold" era. These observations, together with observations at other IR wavelengths, are crucial to characterise the atmosphere of the planet HD189733b. Previous analyses of the same datasets reported discrepant results, hence the necessity of the reanalyses. The method we used here is based on the Independent Component Analysis (ICA) statistical technique, which ensures a high degree of objectivity. The use of ICA to detrend single photometric observations in a self-consistent way is novel in the literature. The advantage of our reanalyses over previous work is that we do not have to make any assumptions on the structure of the unknown instrumental systematics. Such "admission of ignorance" may result in larger error bars than reported in the literature, up to a factor 1.6. This is a worthwhile trade-off for much higher objectivity, necessary for trustworthy claims. Our main results are (1) improved and robust values of orbital and stellar parameters, (2) new measurements of the transit depths at 3.6m, (3) consistency between the parameters estimated from the two observations, (4) repeatability of the measurement within the photometric level of ~2 x10^-4 in the IR, (5) no evidence of stellar variability at the same photometric level within 1 year.

Read more (120kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
HD 189733
Permalink  
 

Title: The corona of HD 189733 and its X-ray activity
Author: I. Pillitteri, S. J. Wolk, J. Lopez-Santiago, H. M. Guenther, S. Sciortino, O. Cohen, V. Kashyap, J. J. Drake

Here we report on the X-ray activity of the primary star, HD189733 A, using a new XMM-Newton observation and a comparison with the previous X-ray observations. The spectrum in the quiescent intervals is described by two temperatures at 0.2 keV and 0.7 keV, while during the flares a third component at 0.9 keV is detected. We obtain estimates of the electron density in the range ne=1.6-13 x 10^10 cm-3 and thus the corona of HD189733 A appears denser than the solar one. {For the third time, we observe a large flare that occurred just after the eclipse of the planet. Together with the flares observed in 2009 and 2011, the events are restricted to a small planetary phase range of \phi=0.55-0.65. Although we do not find conclusive evidence of a significant excess of flares after the secondary transits, we suggest that the planet might trigger such flares when it passes close to locally high magnetic field of the underlying star at particular combinations of stellar rotational phases and orbital planetary phases. For the most recent flares, a wavelet analysis of the light curve suggests a loop of length of four stellar radii at the location of the bright flare, and a local magnetic field of order of 40-100 G, in agreement with the global field measured in other studies. The loop size suggests an interaction of magnetic nature between planet and star, separated by only ~8 stella radii. We also detect the stellar companion (HD 189733 B, ~12" from the primary star) in this XMM observation. Its very low X-ray luminosity (LX=3.4 x 10^26 erg s-1) confirms the old age of this star and of the binary system. The high activity of the primary star is best explained by a transfer of angular momentum from the planet to the star.

Read more (2526kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
RE: HD189733
Permalink  
 

Title: Transit observations of the Hot Jupiter HD 189733b at X-ray wavelengths
Authors: K. Poppenhaeger, J.H.M.M. Schmitt, S.J. Wolk

We present new X-ray observations obtained with Chandra ACIS-S of the HD 189733 system, consisting of a K-type star orbited by a transiting Hot Jupiter and an M-type stellar companion. We report a detection of the planetary transit in soft X-rays with a significantly larger transit depth than observed in the optical. The X-ray data favour a transit depth of 6-8%, versus a broadband optical transit depth of 2.41%. While we are able to exclude several possible stellar origins for this deep transit, additional observations will be necessary to fully exclude the possibility that coronal inhomogeneities influence the result. From the available data, we interpret the deep X-ray transit to be caused by a thin outer planetary atmosphere which is transparent at optical wavelengths, but dense enough to be opaque to X-rays. The X-ray radius appears to be larger than the radius observed at far-UV wavelengths, most likely due to high temperatures in the outer atmosphere at which hydrogen is mostly ionised. We furthermore detect the stellar companion HD 189733B in X-rays for the first time with an X-ray luminosity of log LX = 26.67 erg/s. We show that the magnetic activity level of the companion is at odds with the activity level observed for the planet-hosting primary. The discrepancy may be caused by tidal interaction between the Hot Jupiter and its host star.

Read more (3399kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
HD 189733b
Permalink  
 

Title: Detection of CO absorption in the atmosphere of the hot Jupiter HD 189733b
Authors: Florian Rodler, Martin Kürster, John R. Barnes

With time-series spectroscopic observations taken with the Near Infrared Spectrometer (NIRSPEC) at Keck II, we investigated the atmosphere of the close orbiting transiting extrasolar giant planet, HD 189733b. In particular, we intended to measure the dense absorption line forest around 2.3 micron, which is produced by carbon monoxide (CO). CO is expected to be present in the planetary atmosphere, although no detection of this molecule has been claimed yet. To identify the best suited data analysis method, we created artificial spectra of planetary atmospheres and analysed them by three approaches found in the literature, the deconvolution method, data modelling via chi²-minimisation, and cross-correlation. As a result, we found that cross-correlation and chi²-data modelling show systematically a higher sensitivity than the deconvolution method. We analysed the NIRSPEC data with cross-correlation and detect CO absorption in the day-side spectrum of HD 189733b at the known planetary radial velocity semi-amplitude with 3.4 sigma confidence.

Read more (201kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
RE: HD189733
Permalink  
 

Title: The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations
Authors: F. Pont (1), D. K. Sing (1), N. P. Gibson (2 and 3), S. Aigrain (2), G.Henry (4), N. Husnoo (1) ((1) Exeter, (2) Oxford, (3) ESO, (4) Tennessee State)

The hot Jupiter HD189733b is the most extensively observed exoplanet. Its atmosphere has been detected and characterised in transmission and eclipse spectroscopy, and its phase curve measured at several wavelengths. This paper brings together the results of our campaign to obtain the complete transmission spectrum of the atmosphere of this planet from UV to IR with HST, using the STIS, ACS and WFC3 instruments. We provide a new transmission spectrum across the entire visible and infrared range. The radius ratio in each wavelength band was re-derived, where necessary, to ensure a consistent treatment of the bulk transit parameters and stellar limb-darkening. Special care was taken to correct for both occulted and unocculted star spots, and derive realistic uncertainties. The combined spectrum is very different from the predictions of cloud-free models; it is dominated by Rayleigh scattering over the whole visible and NIR range, the only detected features being narrow Na and K lines. We interpret this as the signature of a haze of condensate grains extending over at least five scale heights. We show that a dust-dominated atmosphere could also explain several puzzling features of the emission spectrum and phase curves, including the large amplitude of the phase curve at 3.6um, the small hot-spot longitude shift and the hot mid-infrared emission spectrum. We discuss possible compositions and derive some first-order estimates for the properties of the putative condensate haze/clouds. We finish by speculating that the dichotomy between the two observationally defined classes of hot Jupiter atmospheres, of which HD189733b and HD209458b are the prototypes, might not be whether they possess a temperature inversion, but whether they are clear or dusty. We also consider the possibility of a continuum of cloud properties between hot Jupiters, young Jupiters and L-type brown dwarfs.

Read more (2453kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: 3.6 and 4.5 Micron Phase Curves and Evidence for Non-Equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b
Authors: Heather A. Knutson, Nikole Lewis, Jonathan J. Fortney, Adam Burrows, Adam P. Showman, Nicolas B. Cowan, Eric Agol, Suzanne Aigrain, David Charbonneau, Drake Deming, Jean-Michel Desert, Gregory W. Henry, Jonathan Langton, Gregory Laughlin

We present new, full-orbit observations of the infrared phase variations of the canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 micron bands using the Spitzer Space Telescope. When combined with previous phase curve observations at 8.0 and 24 micron, these data allow us to characterise the exoplanet's emission spectrum as a function of planetary longitude. We utilise improved methods for removing the effects of intrapixel sensitivity variations and accounting for the presence of time-correlated noise in our data. We measure a phase curve amplitude of 0.1242% ±0.0061% in the 3.6 micron band and 0.0982% ±0.0089% in the 4.5 micron band. We find that the times of minimum and maximum flux occur several hours earlier than predicted for an atmosphere in radiative equilibrium, consistent with the eastward advection of gas by an equatorial super-rotating jet. The locations of the flux minima in our new data differ from our previous observations at 8 micron, and we present new evidence indicating that the flux minimum observed in the 8 micron is likely caused by an over-shooting effect in the 8 micron array. We obtain improved estimates for HD 189733b's dayside planet-star flux ratio of 0.1466% ±0.0040% at 3.6 micron and 0.1787% ±0.0038% at 4.5 micron; these are the most accurate secondary eclipse depths obtained to date for an extrasolar planet. We compare our new dayside and nightside spectra for HD 189733b to the predictions of models from Burrows et al. (2008) and Showman et al. (2009). We find that HD 189733b's 4.5 micron nightside flux is 3.3 sigma smaller than predicted by the Showman et al. models, which assume that the chemistry is in local thermal equilibrium. We conclude that this discrepancy is best-explained by vertical mixing, which should lead to an excess of CO and correspondingly enhanced 4.5 micron absorption in this region.

Read more (785kb, PDF)



__________________
1 2 3 … 7  >  Last»  | Page of 7  sorted by
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Stars/galaxy News -> HD189733


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard