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Sodor A.,Royal Observatory of Belgium | Sodor A.,Konkoly Observatory | Chene A.-N.,Gemini Observatory | De Cat P.,Royal Observatory of Belgium | And 15 more authors.
Astronomy and Astrophysics | Year: 2014

Context. The central star of the HR 8799 system is a γ Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not accurately known because the estimation depends greatly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR 8799. We organized an extensive photometric and multi-site spectroscopic observing campaign to study the pulsations of the central star. Aims. The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47 d nearly continuous photometry obtained with the Microvariability and Oscillations in STars (MOST) space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite for an asteroseismic age determination. Methods. We carried out Fourier analysis of the wide-band photometric time series. Results. We find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f1 = 1.978 d-1.Many multiples of one-ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f 1, where n = {1,2,3,4,5,6,7,8,9,10,13,14,17,18}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47 d time scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae stars. © 2014 ESO.

Hatzes A.P.,Thuringer Landessternwarte Tautenburg | Cochran W.D.,University of Texas at Austin | Endl M.,University of Texas at Austin | Guenther E.W.,Thuringer Landessternwarte Tautenburg | And 15 more authors.
Astronomy and Astrophysics | Year: 2015

Aims. We investigate the nature of the long-period radial velocity variations in α Tau first reported over 20 yr ago. Methods. We analyzed precise stellar radial velocity measurements for α Tau spanning over 30 yr. An examination of the Hα and Ca II λ8662 spectral lines, and Hipparcos photometry was also done to help discern the nature of the long-period radial velocity variations. Results. Our radial velocity data show that the long-period, low amplitude radial velocity variations are long-lived and coherent. Furthermore, Hα equivalent width measurements and Hipparcos photometry show no significant variations with this period. Another investigation of this star established that there was no variability in the spectral line shapes with the radial velocity period. An orbital solution results in a period of P = 628.96 ± 0.90 d, eccentricity, e = 0.10 ± 0.05, and a radial velocity amplitude, K = 142.1 ± 7.2 m? s-1. Evolutionary tracks yield a stellar mass of 1.13 ± 0.11 M·, which corresponds to a minimum companion mass of 6.47 ± 0.53 MJup with an orbital semi-major axis of a = 1.46 ± 0.27 AU. After removing the orbital motion of the companion, an additional period of 520 d is found in the radial velocity data, but only in some time spans. A similar period is found in the variations in the equivalent width of Hα and Ca II. Variations at one-third of this period are also found in the spectral line bisector measurements. The ~520? d period is interpreted as the rotation modulation by stellar surface structure. Its presence, however, may not be long-lived, and it only appears in epochs of the radial velocity data separated by ~10 yr. This might be due to an activity cycle. Conclusions. The data presented here provide further evidence of a planetary companion to α Tau, as well as activity-related radial velocity variations. © ESO, 2015.

Hatzes A.P.,Thuringer Landessternwarte Tautenburg | Zechmeister M.,University of Gottingen | Matthews J.,University of British Columbia | Kuschnig R.,University of Vienna | And 7 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. Our aim is to use precise radial velocity measurements and photometric data to derive the frequency spacing of the p-mode oscillation spectrum of the planet-hosting star β Gem. This spacing along with the interferometric radius for this star can then be used to derive an accurate stellar mass. Methods. We use a long time series of over 60 h of precise stellar radial velocity measurements of β Gem taken with an iodine absorption cell at the echelle spectrograph mounted on the 2 m Alfred Jensch Telescope. We also present complementary photometric data for this star taken with the MOST microsatellite spanning 3.6 d. A Fourier analysis is used to derive the frequencies that are present in each data set. Results. The Fourier analysis of the radial velocity data reveals the presence of up to 17 significant pulsation modes in the frequency interval 10-250 μHz. Most of these fall on a grid of equally-spaced frequencies having a separation of 7.14 ± 0.12 μHz. An analysis of 3.6 days of high precision photometry taken with the MOST space telescopes shows the presence of up to 16 modes, six of which are consistent with modes found in the spectral (radial velocity) data. This frequency spacing is consistent with high overtone radial pulsations; however, until the pulsation modes are identified we cannot be sure if some of these are nonradial modes or even mixed modes. The radial velocity frequency spacing along with angular diameter measurements of β Gem via interferometry results in a stellar mass of M = 1.91 ± 0.09 M ⊙. This value confirms the intermediate mass of the star determined using stellar evolutionary tracks. Conclusions.β Gem is confirmed to be an intermediate mass star. Stellar pulsations in giant stars along with interferometric radius measurements can provide accurate determinations of the stellar mass of planet hosting giant stars. These can also be used to calibrate stellar evolutionary tracks. © 2012 ESO.

Walker G.A.H.,1234 Hewlett Place | Bohlender D.A.,National Research Council Canada | Maier J.P.,University of Basel | Campbell E.K.,University of Basel
Astrophysical Journal Letters | Year: 2015

Based on gas-phase laboratory spectra at 6 K, Campbell et al. confirmed that the diffuse interstellar bands (DIBs) at 9632.7 and 9577.5 Å are due to absorption by the fullerene ion C60 +. They also reported the detection of two other, weaker bands at 9428.5 and 9365.9 Å. These lie in spectral regions heavily contaminated by telluric water vapor lines. We acquired CFHT ESPaDOnS spectra of HD 183143 close to the zenith and chopped with a nearby standard to correct for the telluric line absorption which enabled us to detect a DIB at 9365.9 Å of relative width and strength comparable to the laboratory absorption. There is a DIB of similar strength and FWHM at 9362.5 Å. A stellar emission feature at 9429 Å prevented detection of the 9428.5 Å band. However, a CFHT archival spectrum of HD 169454, where emission is absent at 9429 Å, clearly shows the 9428.5 Å DIB with the expected strength and width. These results further confirm C60 + as a DIB carrier. © 2015. The American Astronomical Society. All rights reserved.

Maier J.P.,University of Basel | Walker G.A.H.,1234 Hewlett Place | Bohlender D.A.,National Research Council Canada | Mazzotti F.J.,University of Basel | And 4 more authors.
Astrophysical Journal | Year: 2011

We present strong evidence that the broad, diffuse interstellar bands (DIBs) at 4881 and 5450 Å are caused by the B1B1 ←-X1A1 transition of H2CCC (l-C 3H2). The large widths of the bands are due to the short lifetime of the B1B1 electronic state. The bands are predicted from absorption measurements in a neon matrix and observed by cavity ring-down in the gas phase and show exact matches to the profiles and wavelengths of the two broad DIBs. The strength of the 5450 Å DIB leads to a l-C3H2 column density of ∼5 × 1014 cm-2 toward HD 183143 and ∼2 × 1014 cm-2 to HD 206267. Despite similar values of E(B - V), the 4881 and 5450 Å DIBs in HD 204827 are less than one-third their strength in HD 183143, while the column density of interstellar C3 is unusually high for HD 204827 but undetectable for HD 183143. This can be understood if C3 has been depleted by hydrogenation to species such as l-C3H2 toward HD 183143. There are also three rotationally resolved sets of triplets of l-C 3H2 in the 6150-6330 Å region. Simulations, based on the derived spectroscopic constants and convolved with the expected instrumental and interstellar line broadening, show credible coincidences with sharp, weak DIBs for the two observable sets of triplets. The region of the third set is too obscured by the α-band of telluric O2. © 2011. The American Astronomical Society.

Campbell E.K.,University of Basel | Holz M.,University of Basel | Maier J.P.,University of Basel | Gerlich D.,TU Chemnitz | And 2 more authors.
Astrophysical Journal | Year: 2016

Recent low-temperature laboratory measurements and astronomical observations have proved that the fullerene cation C+60 is responsible for four diffuse interstellar bands (DIBs). These absorptions correspond to the strongest bands of the lowest electronic transition. The gas phase spectrum below 10 K is reported here for the full wavelength range encompassed by the electronic transition. The absorption spectrum of C+70, with its origin band at 7959.2 A, has been obtained under similar laboratory conditions. Observations made toward the reddened star HD 183143 were used in a specific search for the absorption of these fullerene cations in diffuse clouds. In the case of C+60, one further band in the astronomical spectrum at 9348.5 A is identified, increasing the total number of assigned DIBs to five. Numerous other C+60 absorptions in the laboratory spectrum are found to lie below the astronomical detection limit. Special emphasis is placed on the laboratory determination of absolute absorption cross-sections. For C+60 this directly yields a column density, N (C+60), of 2 1013 cm-2 in diffuse clouds, without the need to rely on theoretical oscillator strengths. The intensity of the C+70 electronic transition in the range 70008000 is spread over many features of similar strength. Absorption cross-section measurements indicate that even for a similar column density, the individual absorption bands of C+70 will be too weak to be detected in the astronomical spectra, which is confirmed giving an upper limit of 2 m to the equivalent width. © 2016. The American Astronomical Society. All rights reserved.

Maier J.P.,University of Basel | Chakrabarty S.,University of Basel | Mazzotti F.J.,University of Basel | Rice C.A.,University of Basel | And 3 more authors.
Astrophysical Journal Letters | Year: 2011

Krełowski etal. have reported a weak, diffuse interstellar band (DIB) at 5069 which appears to match in both mid-wavelength and width the A 2Πu-X 2Πg gas-phase origin absorption band of HC4H+. Here, we present laboratory rotational profiles at low temperatures which are then compared with the 5069 DIB using 0.1 and 0.3 line widths based on a realistic line-of-sight interstellar velocity dispersion. Neither the band shape nor the wavelength of the maximum absorption match, which makes the association of the 5069 DIB with HC4H+ unlikely. The magnetic dipole transition X 2Πg Ω = 1/2→X 2Πg Ω = 3/2 within the ground electronic state which competes with collisional excitation is also considered. In addition, we present the laboratory gas-phase spectrum of the A 2Πu-X 2Πg transition of HC4H+ measured at 25 K in an ion trap and identify further absorption bands at shorter wavelengths for comparison with future DIB data. © 2011. The American Astronomical Society. All rights reserved.

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