Objective Prism Research Articles

Forward modeling of galaxy kinematics in slitless spectroscopy

Context. Slitless spectroscopy has long been considered a complicated and confused technique. Nonetheless, with the advent of Hubble Space Telescope (HST) instruments, characterized by a low sky background level and a high spatial resolution (most notably WFC3), slitless spectroscopy has become an adopted survey tool to study galaxy evolution from space. Aims. We aim to investigate its application to single-object studies to measure not only redshift and integrated spectral features, but also spatially-resolved quantities such as galaxy kinematics. Methods. We built a complete forward model to quantitatively compare actual slitless observations. This model depends on a simplified thin cold disk galaxy description – including flux-distribution, intrinsic-spectrum, and kinematic parameters – and on the instrumental signature. It is used to improve redshifts and constrain basic rotation curve parameters, meaning the plateau velocity v0 (in km s−1) and the central velocity gradient w0 (in km s−1 arcsec−1). Results. The model is tested on selected observations from 3D-HST and GLASS surveys to estimate redshift and kinematic parameters on several galaxies measured with one or more roll angles. Conclusions. Our forward approach makes it possible to mitigate the self-contamination effect, a primary drawback of slitless spectroscopy, and therefore has the potential to increase precision on redshifts. In a limited sample of well-resolved spiral galaxies from HST surveys, it is possible to significantly constrain galaxy rotation curve parameters. This proof-of-concept work is promising for future large slitless spectroscopic surveys, such as Euclid and WFIRST.

Short time-scale variability in the spectrum of the hot B3V star ηUMa

We report the results of observations of short time-scale variability in the Hydrogen Balmer lines and HeI lines in the hot B star ηUMa. Spectral observations were carried out with the low-resolution slitless spectrograph (R∼200) installed on the 60 cm Carl Zeiss telescope in the Andrushivka Observatory, Ukraine. Spectra were obtained with a time resolution in the sub-second range. It has been found that the hot B star ηUMa shows rapid variations in the Hydrogen lines Hβ, Hγ, Hδ, Hε and the Helium lines HeI 5016Å HeI 5047Å, as well as variations in the atmospheric oxygen lines. This can be interpreted that their variations are non-radial pulsations and strong stellar wind.

Resurrecting DFBS into the Virtual Observatory

The Digitized First Byurakan Survey has digitized and processed about 1900 photographic plates from the objective prism surveys conducted in Byurakan by Benjamin Markarian and collaborators in the 1960ies and 1970ies. After digitization, a custom web service was built and operated first in Rome, then in Trieste. However, as astronomical data systems and standards evolved, it became desirable to update the data and build standards-compliant, Virtual Observatory services from it. This contribution reports on the challenges encountered during this migration, the solutions we chose, and the lessons to be learned. It also discusses the use of the resulting services.

Архивы спектральных наблюдений КрАО. Каталоги объектов и изображений

Работа, описанная в данной статье, является продолжением ранее начатых исследований по архивным спектральным наблюдениям, выполненным в Крыму. Она охватывает интервал времени около 90 лет и содержит информацию о спектроскопии с использованием различных телескопов: от широкоугольных астрографов с объективной призмой до главного телескопа КрАО - ЗТШ. Рассмотрена краткая история инструментов, их оборудование. Статья проиллюстрирована возможностями сетевого доступа к каталогам наблюдений на различных инструментах в интерактивном атласе неба Aladin с переадресацией к оригинальным спектрограммам. Для них выполнено преобразование линейных координат отсканированных негативов в шкалу, соответствующую длинам волн. Показаны возможности учета спектральной чувствительности регистрируемых изображений для получения распределения энергии. Особенностью представляемой работы является связь оцифрованных оригинальных наблюдений и результатов их независимой обработки с данными, опубликованными для объектов в журнале "Известия Крымской астрофизической обсерватории".

Modeling with the crowd: Optimizing the human-machine partnership with Zooniverse

AbstractLSST and Euclid must address the daunting challenge of analyzing the unprecedented volumes of imaging and spectroscopic data that these next-generation instruments will generate. A promising approach to overcoming this challenge involves rapid, automatic image processing using appropriately trained Deep Learning (DL) algorithms. However, reliable application of DL requires large, accurately labeled samples of training data. Galaxy Zoo Express (GZX) is a recent experiment that simulated using Bayesian inference to dynamically aggregate binary responses provided by citizen scientists via the Zooniverse crowd-sourcing platform in real time. The GZX approach enables collaboration between human and machine classifiers and provides rapidly generated, reliably labeled datasets, thereby enabling online training of accurate machine classifiers. We present selected results from GZX and show how the Bayesian aggregation engine it uses can be extended to efficiently provide object-localization and bounding-box annotations of two-dimensional data with quantified reliability. DL algorithms that are trained using these annotations will facilitate numerous panchromatic data modeling tasks including morphological classification and substructure detection in direct imaging, as well as decontamination and emission line identification for slitless spectroscopy. Effectively combining the speed of modern computational analyses with the human capacity to extrapolate from few examples will be critical if the potential of forthcoming large-scale surveys is to be realized.

Predicting the Yield of Potential Venus Analogs from TESS and Their Potential for Atmospheric Characterization

Abstract The transit method is biased toward short orbital period planets that are interior to their host star’s habitable zone. These planets are particularly interesting from the perspective of exploring runaway greenhouse scenarios and the possibility of potential Venus analogs. Here, we conduct an analysis of predicted Transiting Exoplanet Survey Satellite (TESS) planet yield estimates produced by Huang et al., as well as the TESS Object of Interest (TOI) list resulting from the observations of sectors 1–13 during Cycle 1 of the TESS primary mission. In our analysis we consider potential terrestrial planets that lie within their host star’s Venus zone. These requirements are then applied to a predicted planetary yield from the TESS primary mission and the TOI list, which results in an estimated 259 Venus analogs by the end of the TESS primary mission, and 46 Venus analogs in the TOI list for sectors 1–13. We also calculate the estimated transmission spectroscopy signal-to-noise ratio (S/N) for Venus analogs from the predicted yield and TOI list if they were to be observed by the Near-Infrared Imager and Slitless Spectrograph on the James Webb Space Telescope, as well as update the S/N cutoff values determined by Kempton et al. Our findings show that the best estimated Venus analogs and TOI Venus analogs with R p < 1.5 R ⊙ have an estimated transmission spectroscopy S/N > 40 while planets with radii 2 R ⊕ < R p < 4 R ⊕ can achieve S/N > 100.

Analysis of the Spectral Characteristics of Triggered Lightning

The spectra with wavelength range of 390 nm to 660 nm of triggered lightning were observed in Guangdong Area using a slitless spectrograph. The characteristics of the lightning spectra during the initial continuous current and return strokes were analyzed, and the differences between the metal section and air section of the lightning channel were compared. The results showed that the metal spectra were contained in the metal section during the initial continuous current. As for the lightning channel of the return strokes, the line spectra for both the metal section and the air section were identical; neither of the two sections contained the metal spectra, but the relative intensity of its emission spectrum was different. Owing to different radiation mechanisms, the spectral structures and luminance of the two sections were not the same. Combined with the current data, it was found that there was a good positive correlation between the total spectral strength and the transferred charge. The total intensity of the lightning channel spectrum increased with the height of the channel, indicating that the radiation sequence of the lightning channel was different. High temporal resolution observations showed that the spectral line duration could be divided into three categories, in which the lines with higher excitation energy appear first and decay rapidly, while those with lower excitation energy appear later but last longer.

Kernel-phase detection limits

Context. The James Webb Space Telescope (JWST) will offer high angular resolution observing capability in the near-infrared with masking interferometry on the Near-Infrared Imager and Slitless Spectrograph (NIRISS), and coronagraphic imaging on the Near-Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI). Full-aperture kernel-phase-based interferometry complements these observing modes by allowing us to probe for companions at small angular resolution while preserving the telescope throughput. Aims. Our goal is to derive both theoretical and operational contrast-detection limits for the kernel-phase analysis of JWST NIRISS full-pupil observations using tools from hypothesis testing theory. The study is immediately applied to observations of faint brown dwarfs with this instrument, but the tools and methods introduced here are applicable in a wide variety of contexts. Methods. We construct a statistically independent set of observable quantities from a collection of aberration-robust kernel phases. Three detection tests based on these observable quantities are designed and analysed, all having the property of guaranteeing a constant false-alarm rate for phase aberrations smaller than about one radian. One of these tests, the likelihood ratio or Neyman-Pearson test, provides a theoretical performance bound for any detection test. Results. The operational detection method considered here is shown to exhibit only marginal power loss with respect to the theoretical bound. In principle, for the test set to a false-alarm probability of 1%, companions at contrasts reaching 103 and separations of 200 mas around objects of magnitude 14.1 are detectable with a probability of 68%. For the brightest objects observable using the full pupil of JWST and NIRISS, contrasts of up to 104 at separations of 200 mas could ultimately be achieved, barring significant wavefront drift. We also provide a statistical analysis of the uncertainties affecting the contrasts and separations that are estimated for the detected companions. Conclusions. The proposed detection method is close to the ultimate bound and offers guarantees on the probability of making a false detection for binaries, as well as on the error bars for the estimated parameters of the binaries that will be detected by JWST NIRISS. This method is not only applicable to JWST NIRISS but to any imaging system with adequate sampling.

Optical variability of faint quasars

AbstractThe variability properties of a quasar sample, spectroscopically complete to magnitude J = 22.0, are investigated on a time baseline of 2 yr, using three different photometric bands (U, J and F). The original sample was obtained using a combination of different selection criteria: colours, slitless spectroscopy and variability, based on a time baseline of 1 yr. The main goals of this work are two-fold: first, to derive the percentage of variable quasars on a relatively short time baseline; secondly, to search for new quasar candidates, missed by the other selection criteria, and thus to estimate the completeness of the spectroscopic sample. In order to achieve these goals, we have extracted all the candidate variable objects from a sample of about 1800 stellar or quasi-stellar objects with limiting magnitude J = 22.50 over an area of about 0.50 deg2. We find that > 65% of all the objects selected as possibly variable are either confirmed quasars or quasar candidates, on the basis of their colours. This percentage increases even further if we exclude from our lists of variable candidates a number of objects equal to that expected on the basis of ‘contamination’ induced by our photometric errors. The percentage of variable quasars in the spectroscopic sample is also high, reaching about 50%. On the basis of these results, we can estimate that the incompleteness of the original spectroscopic sample is < 12%. We conclude that variability analysis of data with small photometric errors can be successfully used as an efficient and independent (or at least auxiliary) selection method in quasar surveys, even when the time baseline is relatively short. Finally, when corrected for the different intrinsic time lags corresponding to a fixed observed time baseline, our data do not show a statistically significant correlation between variability and either absolute luminosity or redshift.

Slitless Solar Imaging Spectroscopy

Abstract Spectrometers provide our most detailed diagnostics of the solar coronal plasma, and spectral data is routinely used to measure the temperature, density, and flow velocity in coronal features. However, spectrographs suffer from a limited instantaneous field of view (IFOV). Conversely, imaging instruments can provide a relatively large IFOV, but extreme-ultraviolet (EUV) multilayer imaging offers very limited spectral resolution. In this paper, we suggest an instrument concept that combines the large IFOV of an imager with the diagnostic capability of a spectrograph, develop a new parametric model to describe the instrument, and evaluate a new method for “deconvolving” the data from such an instrument. To demonstrate the operating principle of this new slitless spectroscopy instrument, actual spectroscopic raster data from the Hinode/EUV Imaging Spectrometer (EIS) spectrometer is used. We assume that observations in multiple spectral orders are obtained, and then use a new inverse problem method to infer the spectral properties. Unlike previous methods, physical constraints and regularization derived from prior knowledge can be naturally incorporated as part of the solution process. We find that the fidelity of the solution is vastly improved compared to previous methods. The errors are typically only a few km s−1 over a large IFOV, with a width of a few hundred pixels and an arbitrarily large height. These errors are not much larger than the errors in current slit spectroscopic instruments with limited IFOV. A further benefit is that the performance of candidate instruments can be optimized for specific scientific objectives. We demonstrate this by deriving optimum values for the spectral dispersion and signal-to-noise ratio.

A contribution of star-forming clumps and accreting satellites to the mass assembly of z ∼ 2 galaxies

ABSTRACT We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved HubbleSpace Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ∼ 1–3. We created continuum and emission line maps and pinpointed residual ‘blobs’ detected after subtracting the galaxy disc. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ∼2 kpc and comparable stellar mass and age as the galaxy discs, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the discs. Furthermore, the extended blobs are typically found at larger distances from the galaxy barycentre than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose, respectively, ∼20 per cent and ≲80 per cent of the galaxy stellar mass, ∼30 per cent and ∼20 per cent of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (M⋆ ≳ 109 M⊙) have lifetimes of ∼650 Myr, and the less massive ones (108 < M⋆ < 109 M⊙) of ∼145 Myr. This supports simulations predicting long-lived clumps (lifetime ≳ 100 Myr). Finally, ≲30 per cent (13 per cent) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ≲10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies.

A visible channel core and the channel structure below the connection point for natural cloud-to-ground lightning

The channel core of natural negative cloud-to-ground lightning was recorded using a high-speed slitless spectrograph, which confirms the corona sheath model of the lightning channel. By analyzing the channel spectra and images at different stages, it is corroborated that the ionic lines in spectra are mainly due to the channel core. Based on the luminescence and spectral characteristics, the connection point of the downward moving leader and the upward connecting leader was located, and it is concluded that the current is the highest at the connection point. Above all, it is discovered that there is no obvious channel core below the connection point, which means that the current is transmitted over the whole channel cross section. This feature is an important basis for investigating the lightning connection process and the physical mechanism of a lightning strike.

The 2018 eruption and long term evolution of the new high-mass Herbig Ae/Be object Gaia-18azl = VES 263

Abstract We have been monitoring, at high cadence, the photometric and spectroscopic evolution of VES 263 following the discovery in 2018 of a brightening labeled as event Gaia-18azl. VES 263 is so far a neglected emission-line object discovered in the 1960s on objective prism plates, tentatively classified as a semi-regular AGB cool giant by automated analysis of ASASSN lightcurves. We have discovered that VES 263 is a bonafide massive pre-Main Sequence object (∼12 M⊙), of the Herbig AeBe type. It is located at 1.68±0.07 kpc distance, within the Cyg OB2 star-forming region, and it is highly reddened (EB − V=1.80±0.05) by interstellar extinction. In quiescence, the spectral energy distribution is dominated by the ∼20,000 K photospheric emission from the central B1II star, and at λ≥6μm by emission from circumstellar warm dust (T≤400○K). The 2018-19 eruption was caused by a marked brightening of the accretion disk around the B1II star as traced by the evolution with time of the integrated flux and the double-peaked profile of emission lines. At the peak of the eruption, the disk has a bulk temperature of ∼7500 K and a luminosity L ≥860 L⊙, corresponding to a mass accretion rate M≥1.1 × 10−5 M⊙ yr−1. Spectroscopic signature of possible bipolar jets (at −700 and +700 km s−1) of variable intensity are found. We have reconstructed from Harvard, Moscow and Sonneberg photographic plates the photometric history of VES 263 from 1896 to 1995.

Characteristic parameters of positive cloud-to-ground lightning channel

The high time-resolved spectra of two natural positive cloud-to-ground (CG) lightning of which one of them contains multiple return strokes have been taken by a high-speed slit-less spectrograph. On combining with the synchronous electric field change waveform, the temperature, electrical conductivity of the return stroke channel, radius of the core current channel and the peak value of current are calculated. The correlation between the peak current and the time interval of five M components which overlapped with the continuous current following the subsequent return stroke R1 of multiple return strokes positive CG lightning were analysed. The results show that the average temperatures of the return stroke channels for two positive CG lightning are about 28,900–29,800 K, the radius of the core current channel is about 0.36–1.01 cm, the estimated peak currents of the return strokes are about 18.6–38.0 kA, which are all larger than the typical values of common negative CG lightning. The peak currents of the M components are positively correlated with the time intervals between them.

Massive Dead Galaxies at z ∼ 2 with HST Grism Spectroscopy. I. Star Formation Histories and Metallicity Enrichment

Abstract Observations have revealed massive ( ) galaxies that were already dead when the universe was only ∼2 Gyr. Given the short time before these galaxies were quenched, their past histories and quenching mechanism(s) are of particular interest. In this paper, we study star formation histories (SFHs) of 24 massive galaxies at 1.6 < z < 2.5. A deep slitless spectroscopy and imaging data set collected from multiple Hubble Space Telescope surveys allows robust determination of their spectral energy distributions and SFHs with no functional assumption on their forms. We find that most of our massive galaxies had formed >50% of their extant masses by ∼1.5 Gyr before the time of observed redshifts, with a trend where more massive galaxies form earlier. Their stellar-phase metallicities are already compatible with those of local early-type galaxies, with a median value of and scatter of ∼0.15 dex. In combination with the reconstructed SFHs, we reveal their rapid metallicity evolution from z ∼ 5.5 to ∼2.2 at a rate of ∼0.2 dex Gyr−1 in . Interestingly, the inferred stellar-phase metallicities are, when compared at half-mass time, ∼0.25 dex higher than observed gas-phase metallicities of star-forming galaxies. While systematic uncertainties remain, this may imply that these quenched galaxies have continued low-level star formation, rather than abruptly terminating their star formation activity, and kept enhancing their metallicity until recently.

Using convolutional neural networks to identify gravitational lenses in astronomical images

Abstract The Euclid telescope, due for launch in 2021, will perform an imaging and slitless spectroscopy survey over half the sky, to map baryon wiggles and weak lensing. During the survey, Euclid is expected to resolve 100 000 strong gravitational lens systems. This is ideal to find rare lens configurations, provided they can be identified reliably and on a reasonable time-scale. For this reason, we have developed a convolutional neural network (CNN) that can be used to identify images containing lensing systems. CNNs have already been used for image and digit classification as well as being used in astronomy for star-galaxy classification. Here, our CNN is trained and tested on Euclid-like and KiDS (Kilo-Degree Survey)-like simulations from the Euclid Strong Lensing Group, successfully classifying 77 per cent of lenses, with an area under the ROC curve of up to 0.96. Our CNN also attempts to classify the lenses in COSMOS Hubble Space Telescope F814W-band images. After convolution to the Euclid resolution, we find we can recover most systems that are identifiable by eye. The python code is available on Github.

Using Saha‐Boltzmann Plot to Diagnose Lightning Return Stroke Channel Temperature

AbstractBased on the high time‐resolved spectra of a cloud‐to‐ground lightning flash with seven return strokes captured by a high‐speed slitless spectrograph, this work was the first to use the Saha‐Boltzmann plot method for the determination of the lightning return stroke channel temperature. The channel temperatures of the seven return strokes ranged from 21370 to 26500 K. Compared with the traditional Boltzmann plot method, the Saha‐Boltzmann plot method can provide more reliable temperature estimation for lightning channel. Analysis of several strong return strokes along the channel showed that the temperature changed little and there was no obvious tendency with increasing height. In addition, it was found that the channel temperature in the late stage of a return stroke was only about 3000–4000 K lower than in the initial stage. This means the channel remains >20000 K during nearly the entire period of the return stroke. This sustained high temperature could be the main cause of lightning‐related disasters.

The current variation along the discharge channel in cloud-to-ground lightning

The spectra of cloud-to-ground lightning return strokes channels are obtained by a slit-less high-speed spectrograph. Based on the positive correlation between discharge current and the intensity of ionic lines in the spectra, variation characteristics of return stroke current along the discharge channel are investigated. The result shows that there are three types of the variation trend for discharge current with the increase of height along the channel, they are exponential attenuation, linear attenuation and basically unchanged, respectively. The attenuation factor is roughly positive correlated with the discharge intensity. During strong discharge process the current tends to decay exponentially. In addition, during return stroke process, the current attenuation gradually flattens with time.

Emission-line Metallicities from the Faint Infrared Grism Survey and VLT/MUSE

Abstract We derive direct-measurement gas-phase metallicities of for 14 low-mass emission-line galaxies at 0.3 < z < 0.8 identified in the Faint Infrared Grism Survey. We use deep slitless G102 grism spectroscopy of the Hubble Ultra Deep Field, dispersing light from all objects in the field at wavelengths between 0.85 and 1.15 μm. We run an automatic search routine on these spectra to robustly identify 71 emission-line sources, using archival data from Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) to measure additional lines and confirm redshifts. We identify 14 objects with 0.3 < z < 0.8 with measurable [O iii]λ4363 Å emission lines in matching VLT/MUSE spectra. For these galaxies, we derive direct electron-temperature gas-phase metallicities with a range of . With matching stellar masses in the range of 107.9 M ⊙ < M ⋆ < 1010.4 M ⊙, we construct a mass–metallicity (MZ) relation and find that the relation is offset to lower metallicities compared to metallicities derived from alternative methods (e.g., R 23, O3N2, N2O2) and continuum selected samples. Using star formation rates derived from the Hα emission line, we calculate our galaxies’ position on the Fundamental Metallicity Relation, where we also find an offset toward lower metallicities. This demonstrates that this emission-line-selected sample probes objects of low stellar masses but even lower metallicities than many comparable surveys. We detect a trend suggesting galaxies with higher Specific Star Formation (SSFR) are more likely to have lower metallicity. This could be due to cold accretion of metal-poor gas that drives star formation, or could be because outflows of metal-rich stellar winds and SNe ejecta are more common in galaxies with higher SSFR.

人工触发闪电通道的辐射特性分析

The spectrum of one triggered lightning with time resolution of 20 μs was observed by using the slit-less spectrograph and the current intensity at the channel bottom was obtained, based on which the radiation characteristics of the lightning spectrum under different current intensities were analyzed. The duration of the spectral line was analyzed according to the excitation energy of the spectral line and the change of the channel current. As a result, the spectral lines were divided into three types. Furthermore, mechanisms of the continuous background radiation of short wavelength and long wavelength were analyzed, respectively. The influences of two radiation mechanisms on continuous background radiation attenuation were researched.