arXiv subjects

Andreas Quirrenbach

Publications and source records attributed to Andreas Quirrenbach.

At least 55 records · Page 3Linked to original sources

arXiv2021

Extreme Precision Radial Velocity Working Group Final Report

Precise mass measurements of exoplanets discovered by the direct imaging or transit technique are required to determine planet bulk properties and potential habitability. Furthermore, it is generally acknowledged that, for the foreseeable future, the Extreme Precision Radial Velocity (EPRV) measurement technique is the only method potentially capable of detecting and measuring the masses and orbits of habitable-zone Earths orbiting nearby F, G, and K spectral-type stars from the ground. In particular, EPRV measurements with a precision of better than approximately 10 cm/s (with a few cm/s stability over many years) are required. Unfortunately, for nearly a decade, PRV instruments and surveys have been unable to routinely reach RV accuracies of less than roughly 1 m/s. Making EPRV science and technology development a critical component of both NASA and NSF program plans is crucial for reaching the goal of detecting potentially habitable Earthlike planets and supporting potential future exoplanet direct imaging missions such as the Habitable Exoplanet Observatory (HabEx) or the Large Ultraviolet Optical Infrared Surveyor (LUVOIR). In recognition of these facts, the 2018 National Academy of Sciences (NAS) Exoplanet Science Strategy (ESS) report recommended the development of EPRV measurements as a critical step toward the detection and characterization of habitable, Earth-analog planets. In response to the NAS-ESS recommendation, NASA and NSF commissioned the EPRV Working Group to recommend a ground-based program architecture and implementation plan to achieve the goal intended by the NAS. This report documents the activities, findings, and recommendations of the EPRV Working Group.

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arXiv2021

On-sky results for the novel integrated micro-lens ring tip-tilt sensor

We present the first on-sky results of the micro-lens ring tip-tilt (MLR-TT) sensor. This sensor utilizes a 3D printed micro-lens ring feeding six multi-mode fibers to sense misaligned light, allowing centroid reconstruction. A tip-tilt mirror allows the beam to be corrected, increasing the amount of light coupled into a centrally positioned single-mode (science) fiber. The sensor was tested with the iLocater acquisition camera at the Large Binocular Telescope in November 2019. The limit on the maximum achieved root mean square reconstruction accuracy was found to be 0.19 $λ$/D in both tip and tilt, of which approximately 50% of the power originates at frequencies below 10 Hz. We show the reconstruction accuracy is highly dependent on the estimated Strehl ratio and simulations support the assumption that residual adaptive optics aberrations are the main limit to the reconstruction accuracy. We conclude that this sensor is ideally suited to remove post-adaptive optics non-common path tip tilt residuals. We discuss the next steps for the concept development, including optimizations of the lens and fiber, tuning of the correction algorithm and selection of optimal science cases.

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arXiv2021

3D-M3: High-spatial resolution spectroscopy with extreme AO and 3D printed micro-lenslets

By combining IFS with ExAO we are now able to resolve objects close to the diffraction-limit of large telescopes, exploring new science cases. We introduce an IFU designed to couple light with a minimal platescale from the SCExAO facility at NIR wavelengths to a SM spectrograph. The IFU has a 3D-printed MLA on top of a custom SM MCF, to optimize the coupling of light into the fiber cores. We demonstrate the potential of the instrument via initial results from the first on-sky runs at the 8.2 m Subaru Telescope with a spectrograph using off-the-shelf optics, allowing for rapid development with low cost.

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arXiv2021

Precise radial velocities of giant stars XV. Mysterious nearly periodic radial velocity variations in the eccentric binary $ε$ Cygni

Using the Hamilton Echelle Spectrograph at Lick Observatory, we have obtained precise radial velocities (RVs) of a sample of 373 G- and K-giant stars over more than 12 years, leading to the discovery of several single and multiple planetary systems. The RVs of the long-period (~53 years) spectroscopic binary $ε$ Cyg (HIP 102488) are found to exhibit additional regular variations with a much shorter period (~291 days). We intend to improve the orbital solution of the $ε$ Cyg system and attempt to identify the cause of the nearly periodic shorter period variations, which might be due to an additional substellar companion. We used precise RV measurements of the K-giant star $ε$ Cyg from Lick Observatory, in combination with a large set of RVs collected more recently with the SONG telescope, as well as archival data sets. Our Keplerian model to the RVs characterizes the orbit of the spectroscopic binary to higher precision than achieved previously, resulting in a semi-major axis of $a = 15.8 \mathrm{AU}$, an eccentricity of $e = 0.93$, and a minimum mass of the secondary of $m \sin i = 0.265 M_\odot$. Additional short-period RV variations closely resemble the signal of a Jupiter-mass planet orbiting the evolved primary component with a period of $291 \mathrm{d}$, but the period and amplitude of the putative orbit change strongly over time. Furthermore, in our stability analysis of the system, no stable orbits could be found in a large region around the best fit. Both of these findings deem a planetary cause of the RV variations unlikely. Most of the investigated alternative scenarios, such as an hierarchical triple or stellar spots, also fail to explain the observed variability convincingly. Due to its very eccentric binary orbit, it seems possible, however, that $ε$ Cyg could be an extreme example of a heartbeat system.

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arXiv2021

An innovative integral field unit upgrade with 3D-printed micro-lenses for the RHEA at Subaru

In the new era of Extremely Large Telescopes (ELTs) currently under construction, challenging requirements drive spectrograph designs towards techniques that efficiently use a facility's light collection power. Operating in the single-mode (SM) regime, close to the diffraction limit, reduces the footprint of the instrument compared to a conventional high-resolving power spectrograph. The custom built injection fiber system with 3D-printed micro-lenses on top of it for the replicable high-resolution exoplanet and asteroseismology spectrograph at Subaru in combination with extreme adaptive optics of SCExAO, proved its high efficiency in a lab environment, manifesting up to ~77% of the theoretical predicted performance.

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arXiv2020

Rubidium transitions as wavelength reference for astronomical Doppler spectrographs

Precise wavelength calibration is a critical issue for high-resolution spectroscopic observations. The ideal calibration source should be able to provide a very stable and dense grid of evenly distributed spectral lines of constant intensity. A new method which satisfies all mentioned conditions has been developed by our group. The approach is to actively measure the exact position of a single spectral line of a Fabry-Perot etalon with very high precision with a wavelength-tuneable laser and compare it to an extremely stable wavelength standard. The ideal choice of standard is the D2 absorption line of Rubidium, which has been used as an optical frequency standard for decades. With this technique, the problem of stable wavelength calibration of spectrographs becomes a problem of how reliably we can measure and anchor one etalon line to the Rb transition. In this work we present our self-built module for Rb saturated absorption spectroscopy and discuss its stability.

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arXiv2019

Focal Plane Tip-Tilt Sensing for Improved Single-Mode Fiber Coupling using a 3D-printed Microlens-Ring

Modern extreme adaptive optics (AO) systems achieving diffraction-limited performance open up new possibilities for instrumentation. Especially important for the fields of spectroscopy and interferometry is that it enables the prospect to couple light into single-mode fibers (SMFs). However, due to their small size, efficient coupling is very sensitive to the quality of the fiber alignment, beam drifts and higher-frequency tip-tilt aberrations caused by telescope mechanics and vibrations. These residual aberrations are not always sensed and corrected by the AO system, leading to unacceptable losses. This is particularly severe for the Extremely Large Telescopes, where their huge structure will mean vibrations increase and optimal AO solutions are even more difficult to implement. We have created a focal plane sensor to correct for residual aberrations by surrounding the SMF with six Multi-mode fibers (MMFs). On each of the MMFs sits a printed freeform lens, making up a six-element micro-lens ring to refract the light into these surrounding MMFs and thus minimizing light loss in the gap between the fiber cores. This means when the beam is near diffraction limited and centered almost all light couples to the SMF. When the beam is misaligned, it couples to the surrounding cores, which are read out by a detector and processed by the DARC software driving a tip-tilt mirror. Currently we are aiming to detect and correct only tip-tilt aberrations. However, choosing to surround the central fiber with six sensing locations potentially allows us to investigate higher order correction modes. Here we present the design and performance our prototype system. This has been designed for use with the iLocater fiber injection system at the LBT and can easily be scaled to larger telescopes. We present test results from the KOOL laboratory and initial integration with the iLocater instrument.

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arXiv2019

Radial-velocity jitter of stars as a function of observational timescale and stellar age

Stars show various amounts of radial velocity (RV) jitter due to varying stellar activity levels. The typical amount of RV jitter as a function of stellar age and observational timescale has not yet been systematically quantified, although it is often larger than the instrumental precision of modern high-resolution spectrographs used for Doppler planet detection and characterization. We aim to empirically determine the intrinsic stellar RV variation for mostly G and K dwarf stars on different timescales and for different stellar ages independently of stellar models. We also focus on young stars ($\lesssim$ 30 Myr), where the RV variation is known to be large. We use archival FEROS and HARPS RV data of stars which were observed at least 30 times spread over at least two years. We then apply the pooled variance (PV) technique to these data sets to identify the periods and amplitudes of underlying, quasiperiodic signals. We show that the PV is a powerful tool to identify quasiperiodic signals in highly irregularly sampled data sets. We derive activity-lag functions for 20 putative single stars, where lag is the timescale on which the stellar jitter is measured. Since the ages of all stars are known, we also use this to formulate an activity--age--lag relation which can be used to predict the expected RV jitter of a star given its age and the timescale to be probed. The maximum RV jitter on timescales of decades decreases from over 500 m/s for 5 Myr-old stars to 2.3 m/s for stars with ages of around 5 Gyr. The decrease in RV jitter when considering a timescale of only 1 d instead of 1 yr is smaller by roughly a factor of 4 for 5 Myr old stars, and a factor of 1.5 for stars with an age of 5 Gyr. The rate at which the RV jitter increases with lag strongly depends on stellar age and ranges from a few days for a few 10 Myr old stars to presumably decades for stars with an age of a few gigayears.

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arXiv2019

ISPY -- NaCo Imaging Survey for Planets around Young stars. Discovery of an M dwarf in the gap between HD 193571 and its debris ring

Context. The interaction between low-mass companions and the debris discs they reside in is still not fully understood. A debris disc can evolve due to self-stirring, a process in which planetesimals can excite their neighbours to the point of destructive collisions. In addition, the presence of a companion could further stir the disc (companion-stirring). Additional information is necessary to understand this fundamental step in the formation and evolution of a planetary system, and at the moment of writing only a handful of systems are known where a companion and a debris disc have both been detected and studied at the same time. Aims. Our primary goal is to augment the sample of these systems and to understand the relative importance between self-stirring and companion-stirring. Methods. In the course of the VLT/NaCo Imaging Survey for Planets around Young stars (ISPY), we observed HD 193571, an A0 debris disc hosting star at a distance of 68 pc with an age between 60 and 170 Myr. We obtained two sets of observations in L' band and a third epoch in H band using the GPI instrument at Gemini-South. Results. A companion was detected in all three epochs at a projected separation of 11 au (0.17 arcsec), and co-motion was confirmed through proper motion analysis. Given the inferred disc size of 120 au, the companion appears to reside within the gap between the host star and the disc. Comparison between the L' and H band magnitude and evolutionary tracks suggests a mass of 0.31 - 0.39 solar masses . Conclusions. We discovered a previously unknown M-dwarf companion around HD 193571, making it the third low-mass stellar object discovered within a debris disc. A comparison to self- and companion-stirring models suggests that the companion is likely responsible for the stirring of the disc.

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arXiv2019

Precise radial velocities of giant stars. XI. Two brown dwarfs in 6:1 mean motion resonance around the K giant star $ν$ Ophiuchi

We present radial-velocity (RV) measurements for the K giant $ν$ Oph (= HIP88048, HD163917, HR6698), which reveal two brown dwarf companions with a period ratio close to 6:1. For our orbital analysis we use 150 precise RV measurements taken at Lick Observatory between 2000 and 2011, and we combine them with RV data for this star available in the literature. Using a stellar mass of $M = 2.7\,M_\odot$ for $ν$ Oph and applying a self-consistent N-body model we estimate the minimum dynamical companion masses to be $m_1\sin i \approx 22.2\,M_{\mathrm{Jup}}$ and $m_2\sin i \approx 24.7\,M_{\mathrm{Jup}}$, with orbital periods $P_1 \approx 530$ d and $P_2 \approx 3185$ d. We study a large set of potential orbital configurations for this system, employing a bootstrap analysis and a systematic $χ_ν^2$ grid-search coupled with our dynamical fitting model, and we examine their long-term stability. We find that the system is indeed locked in a 6:1 mean motion resonance (MMR), with $Δω$ and all six resonance angles $θ_{1}, \ldots, θ_{6}$ librating around 0$^\circ$. We also test a large set of coplanar inclined configurations, and we find that the system will remain in a stable resonance for most of these configurations. The $ν$ Oph system is important for probing planetary formation and evolution scenarios. It seems very likely that the two brown dwarf companions of $ν$ Oph formed like planets in a circumstellar disk around the star and have been trapped in a MMR by smooth migration capture.

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arXiv2019

Orbital relaxation and excitation of planets tidally interacting with white dwarfs

Observational evidence of white dwarf planetary systems is dominated by the remains of exo-asteroids through accreted metals, debris discs, and orbiting planetesimals. However, exo-planets in these systems play crucial roles as perturbing agents, and can themselves be perturbed close to the white dwarf Roche radius. Here, we illustrate a procedure for computing the tidal interaction between a white dwarf and a near-spherical solid planet. This method determines the planet's inward and/or outward drift, and whether the planet will reach the Roche radius and be destroyed. We avoid constant tidal lag formulations and instead employ the self-consistent secular Darwin-Kaula expansions from Boué & Efroimsky (2019), which feature an arbitrary frequency dependence on the quality functions. We adopt wide ranges of dynamic viscosities and spin rates for the planet in order to straddle many possible outcomes, and provide a foundation for the future study of individual systems with known or assumed rheologies. We find that: (i) massive Super-Earths are destroyed more readily than minor planets (such as the ones orbiting WD 1145+017 and SDSS J1228+1040), (ii) low-viscosity planets are destroyed more easily than high-viscosity planets, and (iii) the boundary between survival and destruction is likely to be fractal and chaotic.

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arXiv2019

A planetesimal orbiting within the debris disc around a white dwarf star

Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. We report a stable 123.4min periodic variation in the strength and shape of the CaII emission line profiles originating from the debris disc around the white dwarf SDSSJ122859.93+104032.9. We interpret this short-period signal as the signature of a solid body held together by its internal strength.

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arXiv2019

Precise radial velocities of giant stars. XII. Evidence against the proposed planet Aldebaran b

Radial-velocity variations of the K giant star Aldebaran ($α$ Tau) were first reported in the early 1990s. After subsequent analyses, the radial-velocity variability with a period of $\sim 629\,\mathrm{d}$ has recently been interpreted as caused by a planet of several Jovian masses. We want to further investigate the hypothesis of an extrasolar planet around Aldebaran. We combine 165 new radial-velocity measurements from Lick Observatory with seven already published data sets comprising 373 radial-velocity measurements. We perform statistical analyses and investigate whether a Keplerian model properly fits the radial velocities. We also perform a dynamical stability analysis for a possible two-planet solution. As best Keplerian fit to the combined radial-velocity data we obtain an orbit for the hypothetical planet with a smaller period ($P=607\,\mathrm{d}$) and a larger eccentricity ($e=0.33 \pm 0.04$) than the previously proposed one. However, the residual scatter around that fit is still large, with a standard deviation of $117\,\mathrm{ms}^{-1}$. In 2006/2007, the statistical power of the $\sim 620\,\mathrm{d}$ period showed a temporary but significant decrease. Plotting the growth of power in reverse chronological order reveals that a period around $620\,\mathrm{d}$ is clearly present in the newest data but not in the data taken before $\sim$ 2006. Furthermore, an apparent phase shift between radial-velocity data and orbital solution is observable at certain times. A two-planet Keplerian fit matches the data considerably better than a single-planet solution, but poses severe dynamical stability issues. The radial-velocity data from Lick Observatory do not further support but in fact weaken the hypothesis of a substellar companion around Aldebaran. Oscillatory convective modes might be a plausible alternative explanation of the observed radial-velocity variations.

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arXiv2018

Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b

Hot gas giant exoplanets can lose part of their atmosphere due to strong stellar irradiation, affecting their physical and chemical evolution. Studies of atmospheric escape from exoplanets have mostly relied on space-based observations of the hydrogen Lyman-α line in the far ultraviolet which is strongly affected by interstellar absorption. Using ground-based high-resolution spectroscopy we detect excess absorption in the helium triplet at 1083 nm during the transit of the Saturn-mass exoplanet WASP-69b, at a signal-to-noise ratio of 18. We measure line blue shifts of several km/s and post transit absorption, which we interpret as the escape of part of the atmosphere trailing behind the planet in comet-like form. [Additional notes by authors: Furthermore, we provide upper limits for helium signals in the atmospheres of the exoplanets HD 209458b, KELT-9b, and GJ 436b. We investigate the host stars of all planets with detected helium signals and those of the three planets we derive upper limits for. In each case we calculate the X-ray and extreme ultraviolet flux received by these planets. We find that helium is detected in the atmospheres of planets (orbiting the more active stars and) receiving the larger amount of irradiation from their host stars.]

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arXiv2018

Micro-lens array as tip-tilt sensor for single-mode fiber coupling

We introduce a design for a tip-tilt sensor with integrated single-mode fiber coupling for use with the front-end prototype of the iLocater spectrograph at the Large Binocular Telescope to detect vibrations that occur within the optical train. This sensor is made up of a micro-lens array printed on top of a fiber bundle consisting of a central single-mode fiber and six surrounding multi-mode fibers. The design in based on a previous prototype that utilized a multi-core fiber with seven single-mode fibers. With this updated design, we are able to achieve a better sensing throughput. We report on the modeled performance: if the beam is perfectly aligned, 69% light is coupled into the central single-mode fiber feeding the scientific instrument. When the beam is not aligned, some of the light will be coupled into the outer sensing fibers, providing the position of the beam for tip-tilt correction. For this design we show that there is a linear response in the sensing fibers when the beam is subject to tip-tilt movement. Furthermore we introduce an adaptive optics testbed, which we call the Koenigstuhl Observatory Opto-mechatronics Laboratory (KOOL), this testbed currently simulates vibrations at the Large Binocular Telescope, and in collaboration we have extended it to allow single-mode fiber coupling tests.

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arXiv2018

Optimizing astrophotonic spatial reformatters using simulated on-sky performance

One of the most useful techniques in astronomical instrumentation is image slicing. It enables a spectrograph to have a more compact angular slit, whilst retaining throughput and increasing resolving power. Astrophotonic components like the photonic lanterns and photonic reformatters can be used to replace bulk optics used so far. This study investigates the performance of such devices using end-to-end simulations to approximate realistic on-sky conditions. It investigates existing components, tries to optimize their performance and aims to understand better how best to design instruments to maximize their performance. This work complements the recent work in the field and provides an estimation for the performance of the new components.

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arXiv2018

NAIR: Novel Astronomical Instrumentation through photonic Reformatting

The project "Novel Astronomical Instrumentation through photonic Reformatting" is a DFG-funded collaboration to exploit the recognized potential of photonics solutions for a radically new approach to astronomical instrumentation for optical/infrared high precision spectroscopy and high angular resolution imaging. We present a project overview and initial development results from our Adaptive Optics-photonic test bed, Ultrafast Laser Inscribed waveguides for interferometric beam combination and 3D printing structures for astronomical instrumentation. The project is expected to lead to important technological breakthroughs facilitating uniquely functionality and technical solutions for the next generation of instrumentation.

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arXiv2018

Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search

The determination of accurate stellar parameters of giant stars is essential for our understanding of such stars in general and as exoplanet host stars in particular. Precise stellar masses are vital for determining the lower mass limit of potential substellar companions with the radial velocity method. Our goal is to determine stellar parameters, including mass, radius, age, surface gravity, effective temperature and luminosity, for the sample of giants observed by the Lick planet search. Furthermore, we want to derive the probability of these stars being on the horizontal branch (HB) or red giant branch (RGB), respectively. We compare spectroscopic, photometric and astrometric observables to grids of stellar evolutionary models using Bayesian inference. We provide tables of stellar parameters, probabilities for the current post-main sequence evolutionary stage, and probability density functions for 372 giants from the Lick planet search. We find that $81\%$ of the stars in our sample are more probably on the HB. In particular, this is the case for 15 of the 16 planet host stars in the sample. We tested the reliability of our methodology by comparing our stellar parameters to literature values and find very good agreement. Furthermore, we created a small test sample of 26 giants with available asteroseismic masses and evolutionary stages and compared these to our estimates. The mean difference of the stellar masses for the 24 stars with the same evolutionary stages by both methods is only $\langleΔM\rangle=0.01\pm0.20\;\mathrm{M_\odot}$. We do not find any evidence for large systematic differences between our results and estimates of stellar parameters based on other methods. In particular we find no significant systematic offset between stellar masses provided by asteroseismology to our Bayesian estimates based on evolutionary models.

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