| 1. |
- Boldt-Christmas, Linn, et al.
(författare)
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Optimising spectroscopic observations of transiting exoplanets
- 2024
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 683
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Tidskriftsartikel (refereegranskat)abstract
- Context. When observing the atmospheres of transiting exoplanets using high-resolution spectroscopy, the aim is to detect well-resolved spectral features with high signal-to-noise ratios (S/Ns), as is possible today with modern spectrographs. However, obtaining such high-quality observations comes with a trade-off: a lower cadence of fewer, longer exposures across the transit collects more photons thanks to reduced overheads, enhancing the S/N of each observation, while a higher cadence of several shorter exposures minimises spectral feature smearing due to the continuously changing radial velocity of the planet.Aims. Considering that maximising S/N and minimising smearing are both beneficial to analysis, there is a need to identify the optimal compromise between the two for a given target. In this work, we aim to establish where this compromise lies for a typical exoplanet transit observation in order to benefit future data collection and subsequent interpretation.Methods. We modelled real transit events based on targets as they would be observed with VLT/CRIRES+ at Paranal Observatory, Chile. Creating four hypothetical scenarios, we simulated each set of transmission spectra across 100 realisations of the same transit event in order to vary the time resolution only. We removed telluric and stellar lines from these data sets using the SYSREM algorithm and analysed them through cross-correlation with model templates, measuring how successfully each time resolution and case detected the planetary signal and exploring how the results vary.Results. We demonstrate that there is a continuous change in the significance of the cross-correlation detection based on the trade-off between high and low time resolutions, and that, averaged over a large number of realisations, the function of this significance has clear maxima. The strength and location of these maxima vary depending on, for example, planet system parameters, instrumentation, and the number of removal iterations. We discuss why observers should therefore take several factors into account using a strategy akin to the 'exposure triangle' employed in traditional photography where a balance must be struck by considering the full context of the observation. Our method is robust and may be employed by observers to estimate the best observational strategies for other targets.
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| 2. |
- Casagrande, Luca, et al.
(författare)
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The GALAH survey : effective temperature calibration from the InfraRed Flux Method in the Gaia system
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 507:2, s. 2684-2696
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Tidskriftsartikel (refereegranskat)abstract
- In order to accurately determine stellar properties, knowledge of the effective temperature of stars is vital. We implement Gaia and 2MASS photometry in the InfraRed Flux Method and apply it to over 360000 stars across different evolutionary stages in the GALAH DR3 survey. We derive colour-effective temperature relations that take into account the effect of metallicity and surface gravity over the range 4000K ⪅ T-eff ⪅ 8000 K, from very metal-poor stars to supersolar metallicities. The internal uncertainty of these calibrations is of order 40-80 K depending on the colour combination used. Comparison against solar-twins, Gaia benchmark stars, and the latest interferometric measurements validates the precision and accuracy of these calibrations from F to early M spectral types. We assess the impact of various sources of uncertainties, including the assumed extinction law, and provide guidelines to use our relations. Robust solar colours are also derived.
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| 3. |
- Hahlin, Axel, et al.
(författare)
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Determination of small-scale magnetic fields on Sun-like stars in the near-infrared using CRIRES
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 675
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Tidskriftsartikel (refereegranskat)abstract
- Aims: We aim to characterise the small-scale magnetic fields of a sample of 16 Sun-like stars and investigate the capabilities of the newly upgraded near-infrared (NIR) instrument CRIRES+ at the Very Large Telescope in the context of small-scale magnetic field studies. Our targets also had their magnetic fields studied with optical spectra, which allowed us to compare magnetic field properties at different spatial scales on the stellar surface and to contrast small-scale magnetic field measurements at different wavelengths.Methods: We analysed the Zeeman broadening signature for six magnetically sensitive and insensitive Fe I lines in the H-band to measure small-scale magnetic fields on the stellar surfaces of our sample. We used polarised radiative transfer modelling and non-local thermodynamic equilibrium departure coefficients in combination with Markov chain Monte Carlo sampling to determine magnetic field characteristics and non-magnetic stellar parameters. We used two different approaches to describe the small-scale magnetic fields. The first is a two-component model with a single magnetic region and a free magnetic field strength. The second model contains multiple magnetic components with fixed magnetic field strengths.Results: We found average magnetic field strengths ranging from & SIM;0.4 kG down to < 0.1 kG. The results align closely with other results from high-resolution NIR spectrographs, such as SPIRou. It appears that the typical magnetic field strength in the magnetic region is slightly stronger than 1.3 kG, and for most stars in our sample, this strength is between 1 and 2 kG. We also found that the small-scale fields correlate with the large-scale fields and that the small-scale fields are at least ten times stronger than the large-scale fields inferred with Zeeman Doppler imaging. The two- and multi-component models produce systematically different results, as the strong fields from the multi-component model increase the obtained mean magnetic field strength. When comparing our results with the optical measurements of small-scale fields, we found a systematic offset two to three times stronger than fields in the optical results. This discrepancy cannot be explained by uncertainties in stellar parameters. Care should therefore be taken when comparing results obtained at different wavelengths until a clear cause can be established.
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| 4. |
- Hahlin, Axel, et al.
(författare)
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Multi-scale magnetic field investigation of the M-dwarf eclipsing binary CU Cancri
- 2024
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 684
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Tidskriftsartikel (refereegranskat)abstract
- Aims: We aim to characterise the magnetic field of the eclipsing binary CU Cancri, which consists of two M-dwarf components. The determination of the magnetic field parameters of this target enables comparisons with both observations of similar stars and theoretical predictions of the magnetic field strength in CU Cnc. The target therefore provides an excellent opportunity to test our understanding of the generation of magnetic fields in low-mass stars and its impact on stellar structure.Methods: We used spectropolarimetric observations obtained with ESPaDOnS at the CFHT to investigate the magnetic properties of CU Cnc. To improve the signal, we used least-squares deconvolution (LSD) to create average line profiles. From these LSD profiles, we extracted information about the radial velocities of the components, significantly expanding the number of radial velocity measurements available and allowing for a determination of the orbital parameters. Stokes V LSD profiles were used with Zeeman Doppler imaging to obtain the large-scale magnetic field structures of the two components. We also used detailed polarised radiative transfer modelling to investigate the small-scale fields, by Zeeman-splitting magnetically sensitive Ti I lines in non-polarised spectra.Results: We obtain both the small- and large-scale magnetic field properties of the two components. The large-scale fields are dominantly poloidal, and both components have an average strength of approximately 100 G. This analysis of the large-scale fields likely suffers from some amount of hemisphere degeneracy due to the high inclination of the target, which would cause the large-scale field strength of the components to be underestimated. Both components also show unusual magnetic field configurations compared to stars with similar parameters: the primary is weakly axisymmetric (∼10%), and the secondary has a strong toroidal contribution (∼20%). The small-scale fields are significantly stronger, 3.1 and 3.6 kG for the primary and secondary, respectively. This measurement is in excellent agreement with surface field strength predictions for CU Cnc from magneto-convective stellar evolution models. These results indicate that magnetic fields could play a significant role in the radius inflation due to convective inhibition.
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| 5. |
- Hansen, Jonah T., et al.
(författare)
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Pyxis : a ground-based demonstrator for formation-flying optical interferometry
- 2023
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Ingår i: JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS. - : SPIE - The International Society for Optics and Photonics. - 2329-4124 .- 2329-4221. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- In the past few years, there has been a resurgence in studies of space-based optical/ infrared interferometry, particularly with the vision to use the technique to discover and characterize temperate Earth-like exoplanets around solar analogs. One of the key technological leaps needed to make such a mission feasible is demonstrating that formation flying precision at the level needed for interferometry is possible. Here, we present Pyxis, a ground-based demonstrator for a future small satellite mission with the aim to demonstrate the precision metrology needed for spacebased interferometry. We describe the science potential of such a ground-based instrument and detail the various subsystems: three six-axis robots, a multi-stage metrology system, an integrated optics beam combiner, and the control systems required for the necessary precision and stability. We conclude by looking toward the next stage of Pyxis: a collection of small satellites in Earth orbit.
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| 6. |
- Hansen, Jonah T., et al.
(författare)
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The Pyxis Interferometer (I) : Scientific Context, Metrology System and Optical Design
- 2022
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Ingår i: Optical and infrared interferometry and imaging VIII. - : SPIE - International Society for Optical Engineering. - 9781510653481 - 9781510653474
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Konferensbidrag (refereegranskat)abstract
- Optical interferometry from space is arguably the most exciting prospect for high angular resolution astrophysics; including the analysis of exoplanet atmospheres. This was highlighted in the recent ESA Voyage 2050 plan, which pointed out the exciting potential of this technology, but also indicated the critical need for technological demonstrators. Here we present the Pyxis interferometer; a ground-based pathfinder for a CubeSat space interferometer, currently being built at Mt Stromlo Observatory. We outline its technological and scientific potential as the only visible wavelength interferometer in the Southern Hemisphere, and the optical systems designed to provide CubeSat compatible metrology for formation flying.
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| 7. |
- Lesjak, F., et al.
(författare)
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Retrieval of the dayside atmosphere of WASP-43b with CRIRES
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 678
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Tidskriftsartikel (refereegranskat)abstract
- Accurately estimating the C/O ratio of hot Jupiter atmospheres is a promising pathway towards understanding planet formation and migration, as well as the formation of clouds and the overall atmospheric composition. The atmosphere of the hot Jupiter WASP-43b has been extensively analysed using low-resolution observations with HST and Spitzer, but these previous observations did not cover the K band, which hosts prominent spectral features of major carbon-bearing species such as CO and CH4. As a result, the ability to establish precise constraints on the C/O ratio was limited. Moreover, the planet has not been studied at high spectral resolution, which can provide insights into the atmospheric dynamics. In this study, we present the first high-resolution dayside spectra of WASP-43b with the new CRIRES+ spectrograph. By observing the planet in the K band, we successfully detected the presence of CO and provide evidence for the existence of H2O using the cross-correlation method. This discovery represents the first direct detection of CO in the atmosphere of WASP-43b. Furthermore, we retrieved the temperature-pressure profile, abundances of CO and H2O, and a super-solar C/O ratio of 0.78 by applying a Bayesian retrieval framework to the data. Our findings also shed light on the atmospheric characteristics of WASP-43b. We found no evidence for a cloud deck on the dayside, and recovered a line broadening indicative of an equatorial super-rotation corresponding to a jet with a wind speed of similar to 5kms(-1), matching the results of previous forward models and low-resolution atmospheric retrievals for this planet.
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| 8. |
- Rains, Adam, et al.
(författare)
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Cool and data-driven : an exploration of optical cool dwarf chemistry with both data-driven and physical models
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 529:4, s. 3171-3196
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Tidskriftsartikel (refereegranskat)abstract
- Detailed chemical studies of F/G/K - or solar-type - stars have long been routine in stellar astrophysics, enabling studies in both Galactic chemodynamics and exoplanet demographics. However, similar understanding of the chemistry of M and late-K dwarfs - the most common stars in the Galaxy - has been greatly hampered both observationally and theoretically by the complex molecular chemistry of their atmospheres. Here, we present a new implementation of the data-driven Cannon model, modelling Teff, log g, [Fe/H], and [Ti/Fe] trained on low-medium resolution optical spectra (4000-7000 & Aring;) from 103 cool dwarf benchmarks. Alongside this, we also investigate the sensitivity of optical wavelengths to various atomic and molecular species using both data-driven and theoretical means via a custom grid of MARCS synthetic spectra, and make recommendations for where MARCS struggles to reproduce cool dwarf fluxes. Under leave-one-out cross-validation, our Cannon model is capable of recovering Teff, log g, [Fe/H], and [Ti/Fe] with precisions of 1.4 per cent, ±0.04 dex, ±0.10 dex, and ±0.06 dex respectively, with the recovery of [Ti/Fe] pointing to the as-yet mostly untapped potential of exploiting the abundant - but complex - chemical information within optical spectra of cool stars.
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| 9. |
- Wehrhahn, Ansgar, et al.
(författare)
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CRIRES+ detection of H2O and CO in the transmission spectra of WASP-107 b
- 2022
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- WASP-107 b is a warm super-Neptune with a large extended atmosphere orbiting a bright K dwarf of solar composition. The planet's size and the brightness of its stellar host make it highly amenable to atmospheric characterisation, with previous detections of both He and H2O. We observe it here for the first time in high-resolution spectroscopy in the K-band. To obtain a transmission spectrum of the exoplanet atmosphere, we observe a transit event of WASP-107 b for a total of 5.4 hours (2.7 hours in transit) in the K-band with an average SNR = 64 for each exposure using the high-resolution infrared CRIRES+ spectrograph on the Very Large Telescope on Cerro Paranal, Chile. We aim to demonstrate the capabilities of this new instrument for exoplanet characterisation by searching for the presence of molecular features of key chemical species in the atmosphere with spectral lines detectable in this band, such as CO, CO2, H2O, and CH4. The search for particular chemical species is conducted by using the cross-correlation method on the observed spectra. The transit spectroscopy observations are first cleaned from the stellar and telluric features using the SYSREM algorithm, and the remaining spectral information is then compared to a model transmission spectrum. The model transmission spectrum is obtained using the petitRADTRANS code based on expectations for a warm Neptune-class planet and the observed orbital parameters. We report the detection of H2O in the atmosphere of WASP-107 b with 4.71 sigma significance, as well as a detection of CO at 3.46 sigma. The velocities of these detections show signs of atmospheric weather patterns, such as day-to-night-side temperature gradients. We do not detect the presence of CO2 or CH4. Our results confirm the chemical composition of the WASP-107 b's atmosphere and pave the way for efficient atmospheric studies of other planets of the same class. They show that the newly upgraded high-resolution spectrograph CRIRES+ is suitable for exoplanet transit observations. All detections and non-detections are in agreement with previous transmission studies of WASP-107 b based on low-resolution spectroscopy.
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| 10. |
- Yan, F., et al.
(författare)
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CRIRES+ detection of CO emissions lines and temperature inversions on the dayside of WASP-18b and WASP-76b
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 672
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Tidskriftsartikel (refereegranskat)abstract
- The dayside atmospheres of ultra-hot Jupiters (UHJs) are predicted to possess temperature inversion layers with extremely high temperatures at high altitudes. We observed the dayside thermal emission spectra of WASP-18b and WASP-76b with the new CRIRES+ high-resolution spectrograph at near-infrared wavelengths. Using the cross-correlation technique, we detected strong CO emission lines in both planets, which confirms the existence of temperature inversions on their dayside hemispheres. The two planets are the first UHJs orbiting F-type stars with CO emission lines detected; previous detections were mostly for UHJs orbiting A-type stars. Evidence of weak H2O emission signals is also found for both planets. We further applied forward-model retrievals on the detected CO lines and retrieved the temperature-pressure profiles along with the CO volume mixing ratios. The retrieved logarithmic CO mixing ratio of WASP-18b (-2.2(-1.5)(+1.4)) is slightly higher than the value predicted by the self-consistent model assuming solar abundance. For WASP-76b, the retrieved CO mixing ratio (-3.6(-1.6)(+1.8)) is broadly consistent with the value of solar abundance. In addition, we included the equatorial rotation velocity (upsilon(eq)) in the retrieval when analyzing the line profile broadening. The obtained upsilon(eq) is 7.0 +/- 2.9 km s(-1) for WASP-18b and 5.2(-3.0)(+2.5) km s(-1) for WASP-76b, which are consistent with the tidally locked rotational velocities.
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