32 research outputs found
Deciphering the atmosphere of HAT-P-12b: Solving discrepant results
No full textContext. Two independent investigations of the atmosphere of the hot Jupiter HAT-P-12b by two different groups resulted in discrepant solutions. Using broad-band photometry from the ground, one study found a flat and featureless transmission spectrum that was interpreted as gray absorption by dense cloud coverage. The second study made use of Hubble Space Telescope (HST) observations and found Rayleigh scattering at optical wavelengths caused by haze. Aims. The main purpose of this work is to determine the source of this inconsistency and provide feedback to prevent similar discrepancies in future analyses of other exoplanetary atmospheres. Methods. We studied the observed discrepancy via two methods. With further broad-band observations in the optical wavelength regions, we strengthened the previous measurements in precision, and with a homogeneous reanalysis of the published data, we were able to assess the systematic errors and the independent analyses of the two different groups. Results. Repeating the analysis steps of both works, we found that deviating values for the orbital parameters are the reason for the aforementioned discrepancy. Our work showed a degeneracy of the planetary spectral slope with these parameters. In a homogeneous reanalysis of all data, the two literature data sets and the new observations converge to a consistent transmission spectrum, showing a low-Amplitude spectral slope and a tentative detection of potassium absorption
Role of the impact parameter in exoplanet transmission spectroscopy
No full textContext. Transmission spectroscopy is a promising tool for the atmospheric characterization of transiting exoplanets. Because the planetary signal is faint, discrepancies have been reported regarding individual targets.
Aims. We investigate the dependence of the estimated transmission spectrum on deviations of the orbital parameters of the star-planet system that are due to the limb-darkening effects of the host star. We describe how the uncertainty on the orbital parameters translates into an uncertainty on the planetary spectral slope.
Methods. We created synthetic transit light curves in seven different wavelength bands, from the near-ultraviolet to the near-infrared, and fit them with transit models parameterized by fixed deviating values of the impact parameter b. First, we performed a qualitative study to illustrate the effect by presenting the changes in the transmission spectrum slope with different deviations of b. Then, we quantified these variations by creating an error envelope (for centrally transiting, off-center, and grazing systems) based on a derived typical uncertainty on b from the literature. Finally, we compared the variations in the transmission spectra for different spectral types of host stars.
Results. Our simulations show a wavelength-dependent offset that is more pronounced at the blue wavelengths where the limb-darkening effect is stronger. This offset introduces a slope in the planetary transmission spectrum that becomes steeper with increasing b values. Variations of b by positive or negative values within its uncertainty interval introduce positive or negative slopes, thus the formation of an error envelope. The amplitude from blue optical to near-infrared wavelength for a typical uncertainty on b corresponds to one atmospheric pressure scale height and more. This impact parameter degeneracy is confirmed for different host types; K stars present prominently steeper slopes, while M stars indicate features at the blue wavelengths.
Conclusions. We demonstrate that transmission spectra can be hard to interpret, basically because of the limitations in defining a precise impact parameter value for a transiting exoplanet. This consequently limits a characterization of its atmosphere
Low albedos of hot to ultra-hot Jupiters in the optical to near-infrared transition regime
No full textThe depth of a secondary eclipse contains information of both the thermally emitted light component of a hot Jupiter and the reflected light component. If the day side atmosphere of the planet is assumed to be isothermal, it is possible to disentangle both. In this work, we analyzed 11 eclipse light curves of the hot Jupiter HAT-P-32 b obtained at 0.89 μm in the z′ band. We obtained a null detection for the eclipse depth with state-of-the-art precision, −0.01 ± 0.10 ppt. We confirm previous studies showing that a non-inverted atmosphere model is in disagreement to the measured emission spectrum of HAT-P-32 b. We derive an upper limit on the reflected light component, and thus, on the planetary geometric albedo Ag. The 97.5% confidence upper limit is Ag < 0.2. This is the first albedo constraint for HAT-P-32 b, and the first z′ band albedo value for any exoplanet. This finding disfavors the influence of large-sized silicate condensates on the planetary day side. We inferred z′ band geometric albedo limits from published eclipse measurements also for the ultra-hot Jupiters WASP-12 b, WASP-19 b, WASP-103 b, and WASP-121 b, applying the same method. These values consistently point to a low reflectivity in the optical to near-infrared transition regime for hot to ultra-hot Jupiters
Probing the atmosphere of HD189733b with the Na i and K i lines
No full textHigh spectral resolution transmission spectroscopy is a powerful tool to characterize exoplanet atmospheres. Especially for hot Jupiters, this technique is highly relevant, due to their high altitude absorption e.g. from resonant sodium (Na I) and potassium (K I) lines. We resolve the atmospheric K I-absorption on HD189733b with the aim to compare the resolved K I -line and previously obtained high resolution Na I-D-line observations with synthetic transmission spectra. The line profiles suggest atmospheric processes leading to a line broadening of the order of 10 km/s for the Na I-D-lines, and only a few km/s for the K I-line. The investigation hints that either the atmosphere of HD189733b lacks a significant amount of K I or the alkali lines probe different atmospheric regions with different temperature, which could explain the differences we see in the resolved absorption lines
The PEPSI exoplanet transit survey (PETS) I : Investigating the presence of a silicate atmosphere on the super-earth 55 Cnc e
No full textThe study of exoplanets and especially their atmospheres can reveal key insights on their evolution by identifying specific atmospheric species. For such atmospheric investigations, high-resolution transmission spectroscopy has shown great success, especially for Jupiter-type planets. Towards the atmospheric characterization of smaller planets, the super-Earth exoplanet 55 Cnc e is one of the most promising terrestrial exoplanets studied to date. Here, we present a high-resolution spectroscopic transit observation of this planet, acquired with the PEPSI instrument at the Large Binocular Telescope. Assuming the presence of Earth-like crust species on the surface of 55 Cnc e, from which a possible silicate-vapor atmosphere could have originated, we search in its transmission spectrum for absorption of various atomic and ionized species such as Fe, Fe +, Ca, Ca +, Mg, and K, among others. Not finding absorption for any of the investigated species, we are able to set absorption limits with a median value of 1.9 × RP. In conclusion, we do not find evidence of a widely extended silicate envelope on this super-Earth reaching several planetary radii
O-Band silicon photonic transmitters for datacom and computercom interconnects
No full textToday, the datacenter ecosystems are fueling the demand for novel transmitter (TX) technologies complying with the off-board, on-board, and chip-to-chip computing needs. This has set a new class of requirements for the TX infrastructure that should now offer multiple credentials, namely: high-speed, O-band operation for avoiding dispersion compensation in long distances, wavelength-division multiplexing (WDM) capabilities for higher throughput and multicasting/broadcasting support, and tight copackaging with low-power electronics. Silicon (Si) photonic TXs have been extensively studied toward high-speed and WDM TX engines targeting mainly C-band. Only a limited number of Si-Pho O-band TXs have been reported, however with <= 32 Gb/s/channel line-rate capabilities and with a WDM portfolio that has not been fully explored yet. In this paper, we introduce a novel silicon photonic high-speed O-band TX hardware platform that can meet the current datacom and computercom interconnect requirements. We demonstrate a ring modulator (RM) based four-channelWDMTX at 4 x 40 Gb/s non-return-to-zero (NRZ) operation that supports wavelength parallelism in unicast operation but can also pave the way toward WDM TX engines for the post-100 GbE TX era. Moreover, we present a broadband Si Mach-Zehnder modulator employed in a WDM modulation scheme of 2 x 25 Gb/s NRZ signals and demonstrate multicasting when combined with a 8x8 passive arrayed waveguide grating router (AWGR) wavelength router, addressing the broadcasting needs of traffic usually encountered in cache-coherent multisocket settings. Finally, we further demonstrate the tight synergy of O-band Si-RM modulators with high-speed CMOS electronics, presenting an RM-based TX assembly prototype employing a fully depleted silicon-on-insulator CMOS driver, delivering 50-Gb/s NRZ operation
Dual-facet coupling of SOA array on 4-μm silicon-on-insulator implementing a hybrid integrated SOA-MZI wavelength converter
No full textHybrid integration on Silicon-on-Insulator (SOI) has emerged as a practical solution for compact and high-performance Photonic Integrated Circuits (PICs). It aims at combining the cost-effectiveness and CMOS-compatibility benefits of the low-loss SOI waveguide platform with the versatile active optical functions that can be realized by III-V photonic materials. The utilization of SOI, as an integration board, with Îm-scale dimensions allows for an excellent optical mode matching between silicon rib waveguides and active chips, allowing for minimal-loss coupling of the pre-fabricated IIIV components. While dual-facet coupling as well as III-V multi-element array bonding should be employed to enable enhanced active on-chip functions, so far only single side SOA bonding has been reported. In the present communication, we present a novel integration scheme that flip-chip bonds a 6-SOA array on 4-Îm thick SOI technology by coupling both lateral SOA facets to the waveguides, and report on the experimental results of wavelength conversion operation of a dual-element Semiconductor Optical Amplifier - Mach Zehnder Interferometer (SOA-MZI) circuit. Thermocompression bonding was applied to integrate the pre-fabricated SOAs on SOI, with vertical and horizontal alignment performed successfully at both SOA facets. The demonstrated device has a footprint of 8.2mm x 0.3mm and experimental evaluation revealed a 12Gb/s wavelength conversion operation capability with only 0.8dB power penalty for the first SOA-MZI-on-SOI circuit and a 10Gb/s wavelength conversion operation capability with 2 dB power penalty for the second SOA-MZI circuit. Our experiments show how dual facet integration can significantly increase the level of optical functionalities achievable by flip-chip hybrid technology and pave the way for more advanced and more densely PICs.</p
GJ 1214: Rotation period, starspots, and uncertainty on the optical slope of the transmission spectrum
No full textAims. Brightness inhomogeneities in the stellar photosphere (dark spots or bright regions) affect the measurements of the planetary transmission spectrum. To investigate the star spots of the M dwarf GJ 1214, we conducted a multicolor photometric monitoring from 2012 to 2016.
Methods. The time-series photometry was analyzed with the light curve inversion tool StarSi
400 Gb/s silicon photonic transmitter and routing WDM technologies for glueless 8-socket chip-to-chip interconnects
No full textArrayed Waveguide Grating Router (AWGR)-based interconnections for Multi-Socket Server Boards (MSBs) have been identified as a promising solution to replace the electrical interconnects in glueless MSBs towards boosting processing performance. In this article, we present an 8-socket glueless optical flat-topology Wavelength Division Multiplexing (WDM)-based point-to-point (P2P) interconnect pursued within the H2020 ICT project ICT-STREAMS and we report on our latest achievements in the deployment of the constituent silicon (Si)-photonic transmitter and routing building blocks, exploiting experimentally obtained performance metrics for analyzing the 8-socket chip-to-chip (C2C) connectivity in terms of throughput and energy efficiency. We demonstrate an 8-channel WDM Si-photonic microring-based transmitter (Tx) capable of providing 400 (8 x 50) Gb/s non-return-to-zero (NRZ) Tx capacity and an 8 x 8 Coarse-WDM (CWDM) Si-AWGR with verified cyclic data routing capability in O-band. Following an overview of our recently demonstrated crosstalk (XT)-aware wavelength allocation scheme, that enables fully-loaded AWGR-based interconnects even for typical sub-optimal XT values of silicon integrated CWDM AWGRs, we validate the performance of a full-scale 8-socket interconnect architecture through physical layer simulations exploiting experimentally-verified simulation models for the underlying Si-photonic Tx and routing circuits. This analysis reveals a total aggregate capacity of 1.4 Tb/s for an 8-socket interconnect when operating with 25 Gb/s line-rates, which can scale to 2.8 Tb/s at an energy efficiency of just 5.02 pJ/bit by exploiting the experimentally verified building block performance at 50 Gb/s line. This highlights the perspectives for up to 69% energy savings compared to the standard QuickPath Interconnect (QPI) typically employed in electronic glueless MSB interconnects, while scaling the single-hop flat connectivity from 4- to 8-socket interconnection systems
A 40 Gb/s chip-to-chip interconnect for 8-socket direct connectivity using integrated photonics
No full textWe present an O-band any-to-any chip-to-chip (C2C) interconnection at 40 Gb/s suitable for up to 8-socket direct connectivity in multi-socket server boards, utilizing integrated low-energy photonics for the transceiver and routing functions. The C2C interconnect exploits an Si-based ring modulator as its transmitter and a co-packaged photodiode/transimpedance amplifier enabled receiver interconnected over an 8 x 8 Si-based arrayed waveguide grating router, allowing for a single-hop flat-topology interconnection between eight nodes. A proof-of-concept demonstration of the C2C interconnect is presented at 25 and 40 Gb/s for eight possible routing scenarios, revealing clear eye diagrams at both data rates with extinction ratios of 4.8 +/- 0.3 and 4.38 +/- 0.31 dB, respectively, among the eight routed signals
