arXiv subjects

Andreas Quirrenbach

Publications and source records attributed to Andreas Quirrenbach.

At least 73 records · Page 4Linked to original sources

arXiv2018

The CARMENES search for exoplanets around M dwarfs: A low-mass planet in the temperate zone of the nearby K2-18

K2-18 is a nearby M2.5 dwarf, located at 34 pc and hosting a transiting planet which was first discovered by the {\it K2} mission and later confirmed with {\it Spitzer Space Telescope} observations. With a radius of $\sim 2 \, R_{\oplus}$ and an orbital period of $\sim 33$ days, the planet lies in the temperate zone of its host star and receives stellar irradiation similar to Earth. Here we perform radial velocity follow-up observations with the visual channel of CARMENES with the goal of determining the mass and density of the planet. We measure a planetary semi-amplitude of $K_b \sim 3.5$ \mpersec\ and a mass of $M_b \sim 9 \, M_{\oplus}$, yielding a bulk density around $ρ_b \sim 4 \, \mathrm{g \,cm^{-3}}$. This indicates a low-mass planet with a composition consistent with a solid core and a volatile-rich envelope. A signal at 9 days was recently reported using radial velocity measurements taken with the HARPS spectrograph. This was interpreted as being due to a second planet. We see a weaker, time and wavelength dependent signal in the CARMENES data set and thus favor stellar activity for its origin. \ktwo\ joins the growing group of low-mass planets detected in the temperate zone of M dwarfs. The brightness of the host star in the near-infrared makes the system a good target for detailed atmospheric studies with the {\it James Webb Space Telescope}.

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arXiv2018

Dynamical analysis of the circumprimary planet in the eccentric binary system HD59686

We present a detailed orbital and stability analysis of the HD~59686 binary-star planet system. HD~59686 is a single-lined moderately close ($a_{B} = 13.6\,$AU) eccentric ($e_{B} = 0.73$) binary, where the primary is an evolved K giant with mass $M = 1.9 M_{\odot}$ and the secondary is a star with a minimum mass of $m_{B} = 0.53 M_{\odot}$. Additionally, on the basis of precise radial velocity (RV) data a Jovian planet with a minimum mass of $m_p = 7 M_{\mathrm{Jup}}$, orbiting the primary on a nearly circular S-type orbit with $e_p = 0.05$ and $a_p = 1.09\,$AU, has recently been announced. We investigate large sets of orbital fits consistent with HD 59686's radial velocity data by applying bootstrap and systematic grid-search techniques coupled with self-consistent dynamical fitting. We perform long-term dynamical integrations of these fits to constrain the permitted orbital configurations. We find that if the binary and the planet in this system have prograde and aligned coplanar orbits, there are narrow regions of stable orbital solutions locked in a secular apsidal alignment with the angle between the periapses, $Δω$, librating about $0^\circ$. We also test a large number of mutually inclined dynamical models in an attempt to constrain the three-dimensional orbital architecture. We find that for nearly coplanar and retrograde orbits with mutual inclination $145^\circ \lesssim Δi \leq 180^\circ$, the system is fully stable for a large range of orbital solutions.

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arXiv2017

Theia: Faint objects in motion or the new astrometry frontier

In the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 $\%$ of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision.

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arXiv2016

Precise radial velocities of giant stars IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system

Context: For over 12 yr, we have carried out a precise radial velocity survey of a sample of 373 G and K giant stars using the Hamilton Échelle Spectrograph at Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries. Aims: We aim at detecting and characterizing substellar+stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616). Methods: We obtained high precision radial velocity (RV) measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. In order to discriminate between RV variations due to non-radial pulsation or stellar spots we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to further characterize the system, we obtain high-resolution images with LMIRCam at the Large Binocular Telescope. Results: We report the likely discovery of a giant planet with a mass of $m_{p}~\sin i=6.92_{-0.24}^{+0.18}~M_{Jup}$ orbiting at $a_{p}=1.0860_{-0.0007}^{+0.0006}$ au from the giant star HD 59686 A. Besides the planetary signal, we discover an eccentric ($e_{B}=0.729_{-0.003}^{+0.004}$) binary companion with a mass of $m_{B}~\sin i=0.5296_{-0.0008}^{+0.0011}~M_{Sun}$ orbiting at a semi-major axis of just $a_{B}=13.56_{-0.14}^{+0.18}$ au. Conclusions: The existence of the planet HD 59686 Ab in a tight eccentric binary system severely challenges standard giant planet formation theories and requires substantial improvements to such theories in tight binaries. Otherwise, alternative planet formation scenarios such as second generation planets or dynamical interactions in an early phase of the system's lifetime should be seriously considered in order to better understand the origin of this enigmatic planet.

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arXiv2016

iLocater: A Diffraction-limited Doppler Spectrometer for the Large Binocular Telescope

We are developing a stable and precise spectrograph for the Large Binocular Telescope (LBT) named "iLocater." The instrument comprises three principal components: a cross-dispersed echelle spectrograph that operates in the YJ-bands (0.97-1.30 microns), a fiber-injection acquisition camera system, and a wavelength calibration unit. iLocater will deliver high spectral resolution (R~150,000-240,000) measurements that permit novel studies of stellar and substellar objects in the solar neighborhood including extrasolar planets. Unlike previous planet-finding instruments, which are seeing-limited, iLocater operates at the diffraction limit and uses single mode fibers to eliminate the effects of modal noise entirely. By receiving starlight from two 8.4m diameter telescopes that each use "extreme" adaptive optics (AO), iLocater shows promise to overcome the limitations that prevent existing instruments from generating sub-meter-per-second radial velocity (RV) precision. Although optimized for the characterization of low-mass planets using the Doppler technique, iLocater will also advance areas of research that involve crowded fields, line-blanketing, and weak absorption lines.

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arXiv2016

Performance estimates for spectrographs using photonic reformatters

Using a photonic reformatter to eliminate the effects of conventional modal noise could greatly improve the stability of a high resolution spectrograph. However the regimes where this advantage becomes clear are not yet defined. Here we will look at where modal noise becomes a problem in conventional high resolution spectroscopy and what impact photonic spectrographs could have. We will theoretically derive achievable radial velocity measurements to compare photonic instruments and conventional ones. We will discuss the theoretical and experimental investigations that will need to be undertaken to optimize and prove the photonic reformatting concept.

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arXiv2016

Optimal non-circular fiber geometries for image scrambling in high-resolution spectrographs

Optical fibers are a key component for high-resolution spectrographs to attain high precision in radial velocity measurements. We present a custom fiber with a novel core geometry - a 'D'-shape. From a theoretical standpoint, such a fiber should provide superior scrambling and modal noise mitigation, since unlike the commonly used circular and polygonal fiber cross sections, it shows chaotic scrambling. We report on the fabrication process of a test fiber and compare the optical properties, scrambling performance, and modal noise behavior of the D-fiber with those of common polygonal fibers.

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arXiv2016

State of the Field: Extreme Precision Radial Velocities

The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm/s measurement precision. The presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this precision are summarized here. Beginning with the HARPS spectrograph, technological advances for precision radial velocity measurements have focused on building extremely stable instruments. To reach still higher precision, future spectrometers will need to produce even higher fidelity spectra. This should be possible with improved environmental control, greater stability in the illumination of the spectrometer optics, better detectors, more precise wavelength calibration, and broader bandwidth spectra. Key data analysis challenges for the precision radial velocity community include distinguishing center of mass Keplerian motion from photospheric velocities, and the proper treatment of telluric contamination. Success here is coupled to the instrument design, but also requires the implementation of robust statistical and modeling techniques. Center of mass velocities produce Doppler shifts that affect every line identically, while photospheric velocities produce line profile asymmetries with wavelength and temporal dependencies that are different from Keplerian signals. Exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. Higher precision radial velocity measurements are required to serve as a discovery technique for potentially habitable worlds and to characterize detections from transit missions. The future of exoplanet science has very different trajectories depending on the precision that can ultimately be achieved with Doppler measurements.

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arXiv2015

Precise radial velocities of giant stars VIII. Testing for the presence of planets with CRIRES Infrared Radial Velocities

We have been monitoring 373 very bright (V < 6 mag) G and K giants with high precision optical Doppler spectroscopy for more than a decade at Lick Observatory. Our goal was to discover planetary companions around those stars and to better understand planet formation and evolution around intermediate-mass stars. However, in principle, long-term, g-mode nonradial stellar pulsations or rotating stellar features, such as spots, could effectively mimic a planetary signal in the radial velocity data. Our goal is to compare optical and infrared radial velocities for those stars with periodic radial velocity patterns and to test for consistency of their fitted radial velocity semiamplitudes. Thereby, we distinguish processes intrinsic to the star from orbiting companions as reason for the radial velocity periodicity observed in the optical. Stellar spectra with high spectral resolution have been taken in the H-band with the CRIRES near-infrared spectrograph at ESO's VLT for 20 stars of our Lick survey. Radial velocities are derived using many deep and stable telluric CO2 lines for precise wavelength calibration. We find that the optical and near-infrared radial velocities of the giant stars in our sample are consistent. We present detailed results for eight stars in our sample previously reported to have planets or brown dwarf companions. All eight stars passed the infrared test. We conclude that the planet hypothesis provides the best explanation for the periodic radial velocity patterns observed for these giant stars.

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arXiv2015

Radial Velocity Prospects Current and Future: A White Paper Report prepared by the Study Analysis Group 8 for the Exoplanet Program Analysis Group (ExoPAG)

[Abridged] The Study Analysis Group 8 of the NASA Exoplanet Analysis Group was convened to assess the current capabilities and the future potential of the precise radial velocity (PRV) method to advance the NASA goal to "search for planetary bodies and Earth-like planets in orbit around other stars.: (U.S. National Space Policy, June 28, 2010). PRVs complement other exoplanet detection methods, for example offering a direct path to obtaining the bulk density and thus the structure and composition of transiting exoplanets. Our analysis builds upon previous community input, including the ExoPlanet Community Report chapter on radial velocities in 2008, the 2010 Decadal Survey of Astronomy, the Penn State Precise Radial Velocities Workshop response to the Decadal Survey in 2010, and the NSF Portfolio Review in 2012. The radial-velocity detection of exoplanets is strongly endorsed by both the Astro 2010 Decadal Survey "New Worlds, New Horizons" and the NSF Portfolio Review, and the community has recommended robust investment in PRVs. The demands on telescope time for the above mission support, especially for systems of small planets, will exceed the number of nights available using instruments now in operation by a factor of at least several for TESS alone. Pushing down towards true Earth twins will require more photons (i.e. larger telescopes), more stable spectrographs than are currently available, better calibration, and better correction for stellar jitter. We outline four hypothetical situations for PRV work necessary to meet NASA mission exoplanet science objectives.

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arXiv2014

Precise Radial Velocities of Giant Stars VII. Occurrence Rate of Giant Extrasolar Planets as a Function of Mass and Metallicity

(abridged) We have obtained precise radial velocities for a sample of 373 G and K type giants at Lick Observatory regularly over more than 12 years. Planets have been identified around 15 giant stars; an additional 20 giant stars host planet candidates. We investigate the occurrence rate of substellar companions around giant stars as a function of stellar mass and metallicity. We probe the stellar mass range from about 1 to beyond 3 M_Sun, which is not being explored by main-sequence samples. We fit the giant planet occurrence rate as a function of stellar mass and metallicity with a Gaussian and an exponential distribution, respectively. We find strong evidence for a planet-metallicity correlation among the secure planet hosts of our giant star sample, in agreement with the one for main-sequence stars. However, the planet-metallicity correlation is absent for our sample of planet candidates, raising the suspicion that a good fraction of them might indeed not be planets. Consistent with the results obtained by Johnson for subgiants, the giant planet occurrence rate increases in the stellar mass interval from 1 to 1.9 M_Sun. However, there is a maximum at a stellar mass of 1.9 +0.1/-0.5 M_Sun, and the occurrence rate drops rapidly for masses larger than 2.5-3.0 M_Sun. We do not find any planets around stars more massive than 2.7 M_Sun, although there are 113 stars with masses between 2.7 and 5 M_Sun in our sample (corresponding to a giant planet occurrence rate < 1.6% at 68.3% confidence in that stellar mass bin). We also show that this result is not a selection effect related to the planet detectability being a function of the stellar mass. We conclude that giant planet formation or inward migration is suppressed around higher mass stars, possibly because of faster disk depletion coupled with a longer migration timescale.

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arXiv2014

Kepler-432 b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star

We study the Kepler object Kepler-432, an evolved star ascending the red giant branch. By deriving precise radial velocities from multi-epoch high-resolution spectra of Kepler-432 taken with the CAFE spectrograph at the 2.2m telescope of Calar Alto Observatory and the FIES spectrograph at the Nordic Optical Telescope of Roque de Los Muchachos Observatory, we confirm the planetary nature of the object Kepler-432 b, which has a transit period of 52 days. We find a planetary mass of Mp=5.84 +\- 0.05 Mjup and a high eccentricity of e=0.478 +\- 0.004. With a semi-major axis of a=0.303 +\- 0.007 AU, Kepler-432 b is the first bona fide warm Jupiter detected to transit a giant star. We also find a radial velocity linear trend of 0.44 +\- 0.04 m s$^{-1}$ d$^{-1}$, which suggests the presence of a third object in the system. Current models of planetary evolution in the post-main-sequence phase predict that Kepler-432 b will be most likely engulfed by its host star before the latter reaches the tip of the red giant branch.

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arXiv2014

The Transiting Exoplanet Survey Satellite

The Transiting Exoplanet Survey Satellite (TESS) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its two-year mission, TESS will employ four wide-field optical CCD cameras to monitor at least 200,000 main-sequence dwarf stars with I = 4-13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from one month to one year, depending mainly on the star's ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10-100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every four months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations.

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arXiv2014

Precise radial velocities of giant stars VI. A possible 2:1 resonant planet pair around the K giant star $η$ Cet

We report the discovery of a new planetary system around the K giant $η$ Cet (HIP 5364, HD 6805) based on 118 high-precision optical radial velocities taken at Lick Observatory since July 2000. Since October 2011 an additional nine near-infrared Doppler measurements have been taken using the ESO CRIRES spectrograph (VLT, UT1). The visible data set shows two clear periodicities. Although we cannot completely rule out that the shorter period is due to rotational modulation of stellar features, the infrared data show the same variations as in the optical, which strongly supports that the variations are caused by two planets. Assuming the mass of $η$ Cet to be 1.7 $M_\odot$, the best edge-on coplanar dynamical fit to the data is consistent with two massive planets ($m_b\sin i$ = 2.6 $\pm$ 0.2 $M_{\mathrm{Jup}}$, $m_c\sin i$ = 3.3 $\pm$ 0.2 $M_{\mathrm{Jup}}$), with periods of $P_b$ = 407 $\pm$ 3 days and $P_c$ = 740 $\pm$ 5 days and eccentricities of $e_b$ = 0.12 $\pm$ 0.05 and $e_c$ = 0.08 $\pm$ 0.03. We tested a wide variety of edge-on coplanar and inclined planetary configurations for stability, which agree with the derived radial velocities. We find that in certain coplanar orbital configurations with moderate $e_b$ eccentricity, the planets can be effectively trapped in an anti-aligned 2:1 mean motion resonance. A much larger non-resonant stable region exists in low-eccentricity parameter space, although it appears to be much farther from the best fit than the 2:1 resonant region. In all other cases, the system is categorized as unstable or chaotic. Another conclusion from the coplanar inclined dynamical test is that the planets can be at most a factor of $\sim$ 1.4 more massive than their suggested minimum masses. This stability constraint on the inclination excludes the possibility of two brown dwarfs, and strongly favors a planetary system.

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arXiv2014

The Mice at play in the CALIFA survey: A case study of a gas-rich major merger between first passage and coalescence

We present optical integral field spectroscopy (IFS) observations of the Mice, a major merger between two massive (>10^11Msol) gas-rich spirals NGC4676A and B, observed between first passage and final coalescence. The spectra provide stellar and gas kinematics, ionised gas properties and stellar population diagnostics, over the full optical extent of both galaxies. The Mice provide a perfect case study highlighting the importance of IFS data for improving our understanding of local galaxies. The impact of first passage on the kinematics of the stars and gas has been significant, with strong bars likely induced in both galaxies. The barred spiral NGC4676B exhibits a strong twist in both its stellar and ionised gas disk. On the other hand, the impact of the merger on the stellar populations has been minimal thus far: star formation induced by the recent close passage has not contributed significantly to the global star formation rate or stellar mass of the galaxies. Both galaxies show bicones of high ionisation gas extending along their minor axes. In NGC4676A the high gas velocity dispersion and Seyfert-like line ratios at large scaleheight indicate a powerful outflow. Fast shocks extend to ~6.6kpc above the disk plane. The measured ram pressure and mass outflow rate (~8-20Msol/yr) are similar to superwinds from local ULIRGs, although NGC4676A has only a moderate infrared luminosity of 3x10^10Lsol. Energy beyond that provided by the mechanical energy of the starburst appears to be required to drive the outflow. We compare the observations to mock kinematic and stellar population maps from a merger simulation. The models show little enhancement in star formation during and following first passage, in agreement with the observations. We highlight areas where IFS data could help further constrain the models.

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arXiv2014

Stabilizing a Fabry-Perot etalon to 3 cm/s for spectrograph calibration

We present a method of frequency stabilizing a broadband etalon that can serve as a high-precision wavelength calibrator for an Echelle spectrograph. Using a laser to probe the Doppler-free saturated absorption of the rubidium D2 line, we stabilize one etalon transmission peak directly to the rubidium frequency. The rubidium transition is an established frequency standard and has been used to lock lasers to fractional stabilities of $<10^{-12}$, a level of accuracy far exceeding the demands of radial velocity (RV) searches for exoplanets. We describe a simple setup designed specifically for use at an observatory and demonstrate that we can stabilize the etalon peak to a relative precision of $<10^{-10}$; this is equivalent to 3 cm/s RV precision.

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arXiv2013

NIR imaging spectroscopy of the inner few arcseconds of NGC 4151 with OSIRIS at Keck

We present H- and K-band data from the inner arcsecond of the Seyfert 1.5 galaxy NGC 4151 obtained with the adaptive optics assisted near-infrared imaging field spectrograph OSIRIS at the Keck Observatory. We present the morphology and dynamics of most species detected but focus on the morphology and dynamics of the narrow line region (as traced by emission of [FeII] λ1.644μm), the interplay between plasma ejected from the nucleus (as traced by 21 cm continuum radio data) and hot H2 gas and characterize the detected nuclear HeI$λ2.058 μm absorption feature as a narrow absorption line (NAL) phenomenon.

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arXiv2012

4MOST - 4-metre Multi-Object Spectroscopic Telescope

The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field (>3 square degree, goal >5 square degree), high-multiplex (>1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO 4m-class telescope (VISTA). 4MOST will run permanently on the telescope to perform a 5 year public survey yielding more than 20 million spectra at resolution R~5000 (λ=390-1000 nm) and more than 2 million spectra at R~20,000 (395-456.5 nm & 587-673 nm). The 4MOST design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, eROSITA and Euclid. Initial design and performance estimates for the wide-field corrector concepts are presented. We consider two fibre positioner concepts, a well-known Phi-Theta system and a new R-Theta concept with a large patrol area. The spectrographs are fixed configuration two-arm spectrographs, with dedicated spectrographs for the high- and low-resolution. A full facility simulator is being developed to guide trade-off decisions regarding the optimal field-of-view, number of fibres needed, and the relative fraction of high-to-low resolution fibres. Mock catalogues with template spectra from seven Design Reference Surveys are simulated to verify the science requirements of 4MOST. The 4MOST consortium aims to deliver the full 4MOST facility by the end of 2018 and start delivering high-level data products for both consortium and ESO community targets a year later with yearly increments.

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