V. Sterken, S. Hunziker, Kostas Dialynas, K. Herbst, Aigen Li, L. R. Baalmann, K. Scherer, P. Strub, R. Srama, M. Trieloff, M. Blanc, M. Sommer, M. Rowan‐Robinson, Harald Krüger, F. Effenberger, J. Richardson, D. Malaspina, H. Hsu, M. Horányi, Z. Sternovsky, Jonathan Slavin, J. Linsky, S. Redfield, A. Poppe, J. Szalay, Carey Lisse, E. Provornikova, M. Opher, A. Galli, F. Postberg, A. Czechowski, P. Frisch, William S Kurth, M. Shen, Thomas Chen, Zhengwei Hu, G. Stober, Ingrid Mann, N. Ligterink, Jesse A. Miller, B. Fields, J. Baggeley, P. Brandt
We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavors and programmatic aspects that are important to maintain or develop in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an Interstellar Probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute – through measuring dust – to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it ‘rolls’ into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions.
{"title":"Synergies between interstellar dust and heliospheric science with an Interstellar Probe","authors":"V. Sterken, S. Hunziker, Kostas Dialynas, K. Herbst, Aigen Li, L. R. Baalmann, K. Scherer, P. Strub, R. Srama, M. Trieloff, M. Blanc, M. Sommer, M. Rowan‐Robinson, Harald Krüger, F. Effenberger, J. Richardson, D. Malaspina, H. Hsu, M. Horányi, Z. Sternovsky, Jonathan Slavin, J. Linsky, S. Redfield, A. Poppe, J. Szalay, Carey Lisse, E. Provornikova, M. Opher, A. Galli, F. Postberg, A. Czechowski, P. Frisch, William S Kurth, M. Shen, Thomas Chen, Zhengwei Hu, G. Stober, Ingrid Mann, N. Ligterink, Jesse A. Miller, B. Fields, J. Baggeley, P. Brandt","doi":"10.1093/rasti/rzad034","DOIUrl":"https://doi.org/10.1093/rasti/rzad034","url":null,"abstract":"\u0000 We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavors and programmatic aspects that are important to maintain or develop in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an Interstellar Probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute – through measuring dust – to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it ‘rolls’ into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"224 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133945270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Zhang, Junping Gao, A. Luo, Xia Jiang, Liwen Zhang, Kuang Wu, Bo Qiu
In astronomy, classifying celestial objects based on the spectral data observed by astronomical telescopes is a basic task. So far, most of the work of spectral classification is based on 1D spectral data. However, 2D spectral data, which is the predecessor of 1D spectral data, is rarely used for research. This paper proposes a multi-modal celestial classification network (MAC-Net) based on 2D spectra and photometric images that introduces an attention mechanism. In this work, all 2D spectral data and photometric data were obtained from LAMOST (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope) DR6 and SDSS (Sloan Digital Sky Survey), respectively. The model extracts the features of the blue arm, red arm, and photometric images through three input branches, merges the features at the feature level and sends them to its classifiers for classification. The 2D spectral dataset used in this experiment includes 1223 galaxy spectra, 466 quasar spectra and 1202 star spectra. The same number of photometric images constitute the photometric image dataset. Experimental results show that MAC-Net can classify galaxies, quasars, and stars with a classification precision of 99.2%, 100%, and 97.6%, respectively. And the accuracy reached 98.6%, it means that the similarity between this result and the results obtained by the LAMOST template matching method is 98.6%. The results exceed the performance of the 1D spectrum classification network. At the same time, it also proves the feasibility and effectiveness of directly using 2D spectra to classify celestial bodies by using MAC-Net.
在天文学中，根据天文望远镜观测到的光谱数据对天体进行分类是一项基本任务。目前，光谱分类的大部分工作都是基于一维光谱数据。然而，二维光谱数据作为一维光谱数据的前身，很少被用于研究。提出了一种基于二维光谱和光度图像的多模态天体分类网络(MAC-Net)，该网络引入了注意机制。在这项工作中，所有的二维光谱数据和光度数据分别来自LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) DR6和SDSS (Sloan Digital Sky Survey)。该模型通过三个输入分支提取蓝臂、红臂和光度图像的特征，在特征级进行特征合并，并将其发送给分类器进行分类。本次实验使用的二维光谱数据集包括1223个星系光谱、466个类星体光谱和1202个恒星光谱。相同数量的光度图像构成了光度图像数据集。实验结果表明，MAC-Net可以对星系、类星体和恒星进行分类，分类精度分别达到99.2%、100%和97.6%。准确率达到98.6%，即该结果与LAMOST模板匹配方法得到的结果相似度为98.6%。结果优于一维谱分类网络的性能。同时，也证明了利用MAC-Net直接利用二维光谱进行天体分类的可行性和有效性。
{"title":"A Multi-modal celestial object classification network based on two-dimensional spectrum and photometric image","authors":"M. Zhang, Junping Gao, A. Luo, Xia Jiang, Liwen Zhang, Kuang Wu, Bo Qiu","doi":"10.1093/rasti/rzad026","DOIUrl":"https://doi.org/10.1093/rasti/rzad026","url":null,"abstract":"\u0000 In astronomy, classifying celestial objects based on the spectral data observed by astronomical telescopes is a basic task. So far, most of the work of spectral classification is based on 1D spectral data. However, 2D spectral data, which is the predecessor of 1D spectral data, is rarely used for research. This paper proposes a multi-modal celestial classification network (MAC-Net) based on 2D spectra and photometric images that introduces an attention mechanism. In this work, all 2D spectral data and photometric data were obtained from LAMOST (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope) DR6 and SDSS (Sloan Digital Sky Survey), respectively. The model extracts the features of the blue arm, red arm, and photometric images through three input branches, merges the features at the feature level and sends them to its classifiers for classification. The 2D spectral dataset used in this experiment includes 1223 galaxy spectra, 466 quasar spectra and 1202 star spectra. The same number of photometric images constitute the photometric image dataset. Experimental results show that MAC-Net can classify galaxies, quasars, and stars with a classification precision of 99.2%, 100%, and 97.6%, respectively. And the accuracy reached 98.6%, it means that the similarity between this result and the results obtained by the LAMOST template matching method is 98.6%. The results exceed the performance of the 1D spectrum classification network. At the same time, it also proves the feasibility and effectiveness of directly using 2D spectra to classify celestial bodies by using MAC-Net.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116471133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The origin and evolution of structure in the Universe could be studied in the Dark Ages. The highly redshifted HI signal between 30 < z < 80 is the only observable signal from this era. Human radio interference and ionospheric effects limit Earth-based radio astronomy to frequencies >30 MHz. To observe the low-frequency window with research from compact steep spectrum sources, pulsars, and solar activity, a 200 km baseline lunar far-side radio interferometer has been much discussed. This paper conducts a preliminary site survey of potential far-side craters, which are few in number on the mountainous lunar far-side. Based on LRO LOLA data, 200 m resolution topographic maps of eight far-side sites were produced, and slope and roughness maps were derived from them. A figure of merit was created to determine the optimum site. Three sites are identified as promising. There is a need to protect these sites for astronomy.
宇宙结构的起源和演化可以在黑暗时代进行研究。30 < z < 80之间的高红移HI信号是这个时代唯一可观测的信号。人类无线电干扰和电离层影响限制了地球射电天文学的频率>30兆赫。为了从紧凑的陡峭光谱源、脉冲星和太阳活动中观测低频窗口，人们讨论了一个200公里基线的月球远端射电干涉仪。本文对潜在的远侧陨石坑进行了初步的现场调查，这些陨石坑在多山的月球远侧数量很少。基于LRO LOLA数据，绘制了8个远侧站点的200 m分辨率地形图，并绘制了坡度和粗糙度图。创建了一个价值值来确定最佳地点。三个地点被确定为有希望的。有必要保护这些天文遗址。
{"title":"Lunar Far-Side Radio Arrays: A Preliminary Site Survey","authors":"Zoe A. Le Conte, M. Elvis, Philipp A. Glaser","doi":"10.1093/rasti/rzad022","DOIUrl":"https://doi.org/10.1093/rasti/rzad022","url":null,"abstract":"\u0000 The origin and evolution of structure in the Universe could be studied in the Dark Ages. The highly redshifted HI signal between 30 < z < 80 is the only observable signal from this era. Human radio interference and ionospheric effects limit Earth-based radio astronomy to frequencies >30 MHz. To observe the low-frequency window with research from compact steep spectrum sources, pulsars, and solar activity, a 200 km baseline lunar far-side radio interferometer has been much discussed. This paper conducts a preliminary site survey of potential far-side craters, which are few in number on the mountainous lunar far-side. Based on LRO LOLA data, 200 m resolution topographic maps of eight far-side sites were produced, and slope and roughness maps were derived from them. A figure of merit was created to determine the optimum site. Three sites are identified as promising. There is a need to protect these sites for astronomy.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130194164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. McCulloch, M. D'Cruze, K. Grainge, Michael Keith, S. Melhuish
We describe the design and ground testing of a prototype S-band cryogenic phased array feed. The feed uses 6-mm thick solid aluminium Vivaldi antennas, which were designed using a commercial electromagnetic simulation software. The antennas are designed for easy removal and 40 of them have been integrated into an array. The return loss, inter element coupling and beam patterns have been tested at room temperature and found to agree with simulations. For cryogenic testing the array has been combined with an existing analogue receiver chain and integrated into an cryostat. When tested at 30 K in aperture array mode the system was found to possess a minimum receiver temperature of 12 K. Increasing the number of elements and combining the array with a beamformer would make it a suitable phased array feed (PAF) for radio-astronomy applications.
{"title":"An S-band cryogenic phased array feed for radio astronomy","authors":"M. McCulloch, M. D'Cruze, K. Grainge, Michael Keith, S. Melhuish","doi":"10.1093/rasti/rzad025","DOIUrl":"https://doi.org/10.1093/rasti/rzad025","url":null,"abstract":"\u0000 We describe the design and ground testing of a prototype S-band cryogenic phased array feed. The feed uses 6-mm thick solid aluminium Vivaldi antennas, which were designed using a commercial electromagnetic simulation software. The antennas are designed for easy removal and 40 of them have been integrated into an array. The return loss, inter element coupling and beam patterns have been tested at room temperature and found to agree with simulations. For cryogenic testing the array has been combined with an existing analogue receiver chain and integrated into an cryostat. When tested at 30 K in aperture array mode the system was found to possess a minimum receiver temperature of 12 K. Increasing the number of elements and combining the array with a beamformer would make it a suitable phased array feed (PAF) for radio-astronomy applications.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129188679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Trayford, C. Harrison, R. Hinz, M. Blatt, S. Dougherty, A. Girdhar
We present a novel approach to inspecting galaxy spectra using sound, via their direct audio representation (‘spectral audification’). We discuss the potential of this as a complement to (or stand-in for) visual approaches. We surveyed 58 respondents who use the audio representation alone to rate 30 optical galaxy spectra with strong emission lines. Across three tests, each focusing on different quantities measured from the spectra (signal-to-noise ratio, emission-line width, & flux ratios), we find that user ratings are well correlated with measured quantities. This demonstrates that physical information can be independently gleaned from listening to spectral audifications. We note the importance of context when rating these sonifications, where the order examples are heard can influence responses. Finally, we adapt the method used in this promising pilot study to spectral datacubes. We suggest that audification allows efficient exploration of complex, spatially-resolved spectral data.
{"title":"Inspecting spectra with sound: proof-of-concept & extension to datacubes","authors":"J. Trayford, C. Harrison, R. Hinz, M. Blatt, S. Dougherty, A. Girdhar","doi":"10.1093/rasti/rzad021","DOIUrl":"https://doi.org/10.1093/rasti/rzad021","url":null,"abstract":"\u0000 We present a novel approach to inspecting galaxy spectra using sound, via their direct audio representation (‘spectral audification’). We discuss the potential of this as a complement to (or stand-in for) visual approaches. We surveyed 58 respondents who use the audio representation alone to rate 30 optical galaxy spectra with strong emission lines. Across three tests, each focusing on different quantities measured from the spectra (signal-to-noise ratio, emission-line width, & flux ratios), we find that user ratings are well correlated with measured quantities. This demonstrates that physical information can be independently gleaned from listening to spectral audifications. We note the importance of context when rating these sonifications, where the order examples are heard can influence responses. Finally, we adapt the method used in this promising pilot study to spectral datacubes. We suggest that audification allows efficient exploration of complex, spatially-resolved spectral data.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"114 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116435222","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. V. M. Varma, Anurag Tyagi, Bhushan D. Joshi, Reena Yadav, Pravin A. Chordia, Ghanshyam Kumar, Sakya Sinha, M. Burse, Sreejith Padinhatteri, Rushikesh Deogaonkar, A. Ramaprakash, A. Ghosh, D. Tripathi, Janmejoy Sarkar, K. Sankarasubramanian, K. Nagaraju, K. Vadodariya, R. Kesharwani, Aafaque R. Khan, Manjunath Olekar, Mohamed Azaruddin
The Solar Ultraviolet Imaging Telescope (SUIT) is one of the payloads onboard the Aditya-L1 mission. It will perform full disk imaging of the Sun in the near-Ultraviolet wavelength range of 200-400 nm. This provides near-simultaneous observations of the Sun from the photosphere and chromosphere. A back-illuminated, enhanced UV Charge Coupled Device (CCD) of size 4096 (H) × 4136 (V) pixels, with a pixel size of 12 μm, is used as an imaging element in SUIT. The CCD characterization and the readout electronics development and testing were performed in-house at the Space Astronomy Group (SAG), UR Rao Satellite centre, ISRO. The test setup and procedures are explained and the measured values of various parameters including noise, dark current, gain, linearity, and cross-talk are presented in this paper. The results show a satisfactory performance from the CCD as well as the readout electronics to meet the specifications required by the SUIT payload.
{"title":"The Solar Ultra-Violet Imaging Telescope: Detector characterization and readout electronics testing","authors":"S. V. M. Varma, Anurag Tyagi, Bhushan D. Joshi, Reena Yadav, Pravin A. Chordia, Ghanshyam Kumar, Sakya Sinha, M. Burse, Sreejith Padinhatteri, Rushikesh Deogaonkar, A. Ramaprakash, A. Ghosh, D. Tripathi, Janmejoy Sarkar, K. Sankarasubramanian, K. Nagaraju, K. Vadodariya, R. Kesharwani, Aafaque R. Khan, Manjunath Olekar, Mohamed Azaruddin","doi":"10.1093/rasti/rzad013","DOIUrl":"https://doi.org/10.1093/rasti/rzad013","url":null,"abstract":"\u0000 The Solar Ultraviolet Imaging Telescope (SUIT) is one of the payloads onboard the Aditya-L1 mission. It will perform full disk imaging of the Sun in the near-Ultraviolet wavelength range of 200-400 nm. This provides near-simultaneous observations of the Sun from the photosphere and chromosphere. A back-illuminated, enhanced UV Charge Coupled Device (CCD) of size 4096 (H) × 4136 (V) pixels, with a pixel size of 12 μm, is used as an imaging element in SUIT. The CCD characterization and the readout electronics development and testing were performed in-house at the Space Astronomy Group (SAG), UR Rao Satellite centre, ISRO. The test setup and procedures are explained and the measured values of various parameters including noise, dark current, gain, linearity, and cross-talk are presented in this paper. The results show a satisfactory performance from the CCD as well as the readout electronics to meet the specifications required by the SUIT payload.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115044734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Tennyson, Marco Pezzella, Jingxin Zhang, S. Yurchenko
The ExoMol database currently provides comprehensive line lists for modelling the spectroscopic properties of molecules in hot atmospheres. Extending the spectral range of the data provided to ultraviolet (UV) wavelengths brings into play three processes not currently accounted for in the ExoMol data structure, namely photodissociation, which is an important chemical process in its own right, the opacity contribution due to continuum absorption and predissociation which can lead to significant and observable line broadening effects. Data structures are proposed which will allow these processes to be correctly captured and the (strong) temperature-dependent effects predicted for UV molecular photoabsorption in general and photodissociation in particular to be represented.
{"title":"Data structures for photoadsorption within the ExoMol project","authors":"J. Tennyson, Marco Pezzella, Jingxin Zhang, S. Yurchenko","doi":"10.1093/rasti/rzad014","DOIUrl":"https://doi.org/10.1093/rasti/rzad014","url":null,"abstract":"\u0000 The ExoMol database currently provides comprehensive line lists for modelling the spectroscopic properties of molecules in hot atmospheres. Extending the spectral range of the data provided to ultraviolet (UV) wavelengths brings into play three processes not currently accounted for in the ExoMol data structure, namely photodissociation, which is an important chemical process in its own right, the opacity contribution due to continuum absorption and predissociation which can lead to significant and observable line broadening effects. Data structures are proposed which will allow these processes to be correctly captured and the (strong) temperature-dependent effects predicted for UV molecular photoabsorption in general and photodissociation in particular to be represented.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131033963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We revisit the Hipparcos 2007 re-reduction and find improvements to the catalog by leveraging Gaia EDR3. We show that including a constant residual offset and additional dispersion (two free parameters in total) in the Hipparcos 2007 IAD creates a new catalog with significantly better agreement with Gaia EDR3. The astrometric parameters, after recalibration, have z-scores that follow a unit-Gaussian when measured against Gaia EDR3 values. We have expanded the Python astrometry tool, htof, to recalibrate the IAD on-the-fly. On a second front, we find that a merged set of IAD from the 1997 and 2007 Hipparcos reductions is not possible in an internally consistent manner. This can be understood if Hipparcos 2007 is an improved, but overfit, model to the underlying along-scan data. For this reason, we recommend using the recalibrated Hipparcos 2007 astrometric parameters, or those from the Hipparcos-Gaia Catalog of Accelerations – because the signatures of overfitting are calibrated out. We advise caution in fitting orbits to the IAD from either Hipparcos 2 as-published or the recalibrated version presented here.
{"title":"Statistical properties of Hipparcos 2, caveats on its use, and a recalibration of the Intermediate Astrometric Data","authors":"G. M. Brandt, D. Michalik, Timothy D. Brandt","doi":"10.1093/rasti/rzad011","DOIUrl":"https://doi.org/10.1093/rasti/rzad011","url":null,"abstract":"\u0000 We revisit the Hipparcos 2007 re-reduction and find improvements to the catalog by leveraging Gaia EDR3. We show that including a constant residual offset and additional dispersion (two free parameters in total) in the Hipparcos 2007 IAD creates a new catalog with significantly better agreement with Gaia EDR3. The astrometric parameters, after recalibration, have z-scores that follow a unit-Gaussian when measured against Gaia EDR3 values. We have expanded the Python astrometry tool, htof, to recalibrate the IAD on-the-fly. On a second front, we find that a merged set of IAD from the 1997 and 2007 Hipparcos reductions is not possible in an internally consistent manner. This can be understood if Hipparcos 2007 is an improved, but overfit, model to the underlying along-scan data. For this reason, we recommend using the recalibrated Hipparcos 2007 astrometric parameters, or those from the Hipparcos-Gaia Catalog of Accelerations – because the signatures of overfitting are calibrated out. We advise caution in fitting orbits to the IAD from either Hipparcos 2 as-published or the recalibrated version presented here.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126434601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Quasi-Periodic Eruptions (QPEs) are a rare phenomenon in which the X-ray emission from the nuclei of galaxies shows a series of large amplitude flares. Only a handful of QPEs have been observed but the possibility remains that there are as yet undetected sources in archival data. Given the volume of data available a manual search is not feasible, and so we consider an application of machine learning to archival data to determine whether a set of time-domain features can be used to identify further lightcurves containing eruptions. Using a neural network and 14 variability measures we are able to classify lightcurves with accuracies of greater than $94{{%}}$ with simulated data and greater than $98{{%}}$ with observational data on a sample consisting of 12 lightcurves with QPEs and 52 lightcurves without QPEs. An analysis of 83,531 X-ray detections from the XMM Serendipitous Source Catalogue allowed us to recover lightcurves of known QPE sources and examples of several categories of variable stellar objects.
{"title":"Searching for Quasi-Periodic Eruptions using machine learning","authors":"R. Webbe, A. Young","doi":"10.1093/rasti/rzad015","DOIUrl":"https://doi.org/10.1093/rasti/rzad015","url":null,"abstract":"\u0000 Quasi-Periodic Eruptions (QPEs) are a rare phenomenon in which the X-ray emission from the nuclei of galaxies shows a series of large amplitude flares. Only a handful of QPEs have been observed but the possibility remains that there are as yet undetected sources in archival data. Given the volume of data available a manual search is not feasible, and so we consider an application of machine learning to archival data to determine whether a set of time-domain features can be used to identify further lightcurves containing eruptions. Using a neural network and 14 variability measures we are able to classify lightcurves with accuracies of greater than $94{{%}}$ with simulated data and greater than $98{{%}}$ with observational data on a sample consisting of 12 lightcurves with QPEs and 52 lightcurves without QPEs. An analysis of 83,531 X-ray detections from the XMM Serendipitous Source Catalogue allowed us to recover lightcurves of known QPE sources and examples of several categories of variable stellar objects.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127249158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Regularised least-squares tomography offers a straightforward and efficient imaging method and has seen extensive application across various fields. However, it has a few drawbacks, such as (i) the regularisation imposed during the inversion tends to give a smooth solution, which will fail to reconstruct a multi-scale model well or detect sharp discontinuities, (ii) it requires finding optimum control parameters, (iii) it does not produce a sparse solution. This paper introduces ‘overcomplete tomography’, a novel imaging framework that allows high-resolution recovery with relatively few data points. We express our image in terms of an overcomplete basis, allowing the representation of a wide range of features and characteristics. Following the insight of ‘compressive sensing’, we regularise our inversion by imposing a penalty on the L1 norm of the recovered model, obtaining an image that is sparse relative to the overcomplete basis. We demonstrate our method with a synthetic and a real X-ray tomography example. Our experiments indicate that we can reconstruct a multi-scale model from only a few observations. The approach may also assist interpretation, allowing images to be decomposed into (for example) ‘global’ and ‘local’ structures. The framework presented here can find application across a wide range of fields, including engineering, medical and geophysical tomography.
{"title":"Overcomplete tomography: A novel approach to imaging","authors":"B. Turunçtur, A. Valentine, M. Sambridge","doi":"10.1093/rasti/rzad010","DOIUrl":"https://doi.org/10.1093/rasti/rzad010","url":null,"abstract":"\u0000 Regularised least-squares tomography offers a straightforward and efficient imaging method and has seen extensive application across various fields. However, it has a few drawbacks, such as (i) the regularisation imposed during the inversion tends to give a smooth solution, which will fail to reconstruct a multi-scale model well or detect sharp discontinuities, (ii) it requires finding optimum control parameters, (iii) it does not produce a sparse solution. This paper introduces ‘overcomplete tomography’, a novel imaging framework that allows high-resolution recovery with relatively few data points. We express our image in terms of an overcomplete basis, allowing the representation of a wide range of features and characteristics. Following the insight of ‘compressive sensing’, we regularise our inversion by imposing a penalty on the L1 norm of the recovered model, obtaining an image that is sparse relative to the overcomplete basis. We demonstrate our method with a synthetic and a real X-ray tomography example. Our experiments indicate that we can reconstruct a multi-scale model from only a few observations. The approach may also assist interpretation, allowing images to be decomposed into (for example) ‘global’ and ‘local’ structures. The framework presented here can find application across a wide range of fields, including engineering, medical and geophysical tomography.","PeriodicalId":367327,"journal":{"name":"RAS Techniques and Instruments","volume":"89 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124231632","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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