CCD Frames Research Articles

New astrometric positions for six Jovian irregular satellites using Gaia DR3 in 2016 — 2021

The Jovian system is like a miniature solar system, with the system being more than twice as massive as all the other planets combined and having many natural satellites. Its formation and early evolution had a profound influence on our knowledge of the sculpting of the architecture of the solar system. Astrometric observations are of importance, based on these observations, its orbital dynamics, as well as its origin sometimes, of a solar system object can be determined. We aimed to obtain good astrometric positions of some irregular satellites Elara, Pasiphae, Sinope, Lysithea, Carme and Ananke to refine their orbits and ephemerides, and to understand their dynamics. We have taken, processed and reduced 964 ground-based CCD frames obtained between 2016 and 2021 by the 2.4 m telescope at the Lijiang Station of Yunnan Observatory over 27 nights. Among CCD image processing, the image subtraction technique of ISIS is employed to eliminate star images that are close to or/and almost overlapped with those of our targets in 2019. The star catalog Gaia DR3 is utilized for astrometric calibration, in which a weight scheme is applied to solve more accurate plate model. For all targets, their theoretical positions are retrieved from the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE) ephemeris. Our results show the mean (O - C)s (observed minus computed) of the positional residuals of all targets are −0′′.007 and 0′′.011 in R.A. and Dec., respectively. Their corresponding standard deviations are about 0′′.05 in each direction, except for Ananke (the faintest satellite) with its standard deviation about 0′′.08 in each direction.

Characterization of Instrumental Polarization in the MOPTOP Instrument

MOPTOP is a polarimeter currently installed on the fully robotic 2 m Liverpool Telescope, designed to allow accurate measurements of the variability of the polarization of astronomical objects like gamma-ray bursts and blazars. In this work, we present the characterization of the field position dependent instrumental polarization added by MOPTOP to the acquired images. This characterization is done by the acquisition of images of low polarized standard stars, for different positions over the CCD frame, for the filters BVRIL. These images were reduced using the MOPTOP pipeline, providing us with the q and u Stokes parameters. These values, in turn, were subtracted from the q and u values of the respective star, found in literature, resulting in the spatial distribution of the residual polarization added by the instrument. A plane was fitted to the obtained result, allowing us to calculate the q and u values added by MOPTOP.

Dynamic Micro-Vibration Measurement Based on Orbital Angular Momentum

In this study, we introduce a novel approach for dynamic micro-vibration measurement, employing an Orbital Angular Momentum (OAM) interferometer, where the reference beam is Gaussian (GS) and the measurement beam is OAM. The OAM light reflected back from the target carries information about the target’s vibrations. The interference of the OAM light with Gaussian light generates petal-shaped patterns, and the target’s vibration information can be measured by detecting the rotation angle of these petals. Our proposed method demonstrates enhanced tolerance to misalignment and superior precision. The effects of vibration frequency, CCD frame rates, and Topological Charges (TCs) on measurement accuracy are analyzed thoroughly. Experimental results reveal that the proposed method offers a higher accuracy (up to 22.34 nm) and an extended measurement range of (0–800 cm). These capabilities render our technique highly suitable for applications demanding nanometer-scale resolution in various fields, including precision engineering and advanced optical systems.

Результаты астрометрических наблюдений АСЗ на пулковском 40-см телескопе в обсерватории Ассы-Тургень

We present the results of astrometric observations of two near-Earth asteroids (2005 XY7 and 2007 UM12) performed in September-November 2023 with the 40-cm Pulkovo telescope in the Assy-Turgen observatory. Stellar and asteroid pixel coordinates were calculated by varying the photo center position, background, and flux values for the PSF (point spread function) based on the analysis of the stellar images. The stars within the 4-arcmin asteroid-centered ring were not involved in the astrometric calibration. These stars were used for the asteroid systematic correction calculation. As a result, the internal accuracy of asteroid positions was better than 0.1 arcsec. The estimation of the mean position and the apparent rate components were performed for each set of CCD frames. Finally, the typical accuracy of the coordinates reached values of 0.024 – 0.088 arcsec. In addition, the numerical integration of the asteroid motion was made by varying the components of the state vector and A2-parameter (Yarkovsky acceleration). The unexpected and statistically insignificant A2 value for the 2007 UM12 has been found. It can be explained by the low quality of the data related to the first approach of this asteroid to the Earth and/or the tidal effects that changed the rotational state of the asteroid. The value A2 = (8.1 ± 6.4) · 10−14 a.u. per day2 on the significance boundary has been calculated for 2005 XY7 asteroid. This value does not contradict well-known data for the same size asteroids.

An astrometric approach to measuring the colour of an object

ABSTRACT The colour of a star is a critical feature to reflect its physical property such as the temperature. The colour index is usually obtained via absolute photometry, which is demanding for weather conditions and instruments. In this work, we present an astrometric method to measure the catalogue-matched colour index of an object based on the effect of differential colour refraction (DCR). Specifically, we can observe an object using only one filter or alternately using two different filters. Through the difference of the DCR effect compared with reference stars, the catalogue-matched colour index of an object can be conveniently derived. Hence, we can perform DCR calibration and obtain its accurate and precise positions even if observed with Null filter during a large range of zenith distances, by which the limiting magnitude and observational efficiency of the telescope can be significantly improved. This method takes advantage of the DCR effect and builds a link between astrometry and photometry. In practice, we measure the colour indices and positions of Himalia (the sixth satellite of Jupiter) using 857 CCD frames over 8 nights by two telescopes. Totally, the mean colour index BP − RP (Gaia photometric system) of Himalia is 0.750 ± 0.004 mag. Through the rotational phased colour index analysis, we find two places with their colour indices exceeding the mean ± 3σ.

Searching for single-frame rapid X-ray transients detected with Chandra

ABSTRACT We propose a new method to identify rapid X-ray transients observed with focusing telescopes. They could be statistically significant if three or more photons are detected with Chandra in a single CCD frame within a point-spread-function region out of quiescent background. In the Chandra archive, 11 such events are discovered from regions without point-like sources, after discrimination of cosmic rays and background flares and control of false positives. Among them, two are spatially coincident with extended objects in the Milky Way, one with the Small Magellanic Cloud, and another one with M31; the rest have no or a dim optical counterpart (≳20 mag), and are not clustered on the Galactic plane. Possible physical origins of the rapid transients are discussed, including short gamma-ray bursts (GRBs), short-lived hypermassive neutron stars produced by merger of neutron stars, accreting compact objects in the quiescent state, magnetars, and stellar flares. According to the short GRB event rate density, we expect to have detected $2.3_{-0.6}^{+0.7}$ such events in the Chandra archive. This method would also allow us to reveal quiescent black holes with only a few photons.

Precise Distance Measurement for a Near-Earth Asteroid by the Refined Rotational Reflex Velocity Method

The rotational reflex velocity (RRV) method was proposed by Heinze and Metchev in 2015 and was used to measure the distances of main-belt asteroids (MBAs). Later, Lin et al. generalized this method using spherical astronomy in 2016. The method measures the distances of MBAs using the observations from a single ground-based telescope over two nights. We refined this method and extend it further to the distance measurement of near-Earth asteroids (NEAs). In practice, we measure the distance of the potentially hazardous asteroid (99942) Apophis from the acquired CCD frames using the newly refined method. According to the requirement of the newly refined method, we also simulate the distance measurements of the four typical NEAs, (1221) Amor, (1862) Apollo, (2062) Aten, and (163693) Atira, on their discovery dates and follow-up dates. The measurement results of Apophis based on the newly refined RRV method show that the mean relative errors for the independent exposure frames on the successive two nights is ∼0.08% (about a factor of 2 improvement in comparison with the research of Lin et al.) compared with the distance from JPL ephemeris. Our simulation results also show that this refined method can accurately and precisely measure the distances of newly discovered NEAs in an astrometric way without performing orbital determination. The accurate and precise distances of newly discovered asteroids help us to conveniently evaluate their impact risks within a shorter time, leaving us more time to take defense precautions.

Searching for Variable Stars in the Open Cluster NGC 2355 and Its Surrounding Region

We have investigated the variable stars in the field surrounding NGC 2355 based on the time-series photometric observation data. More than 3000 CCD frames were obtained in the V band spread over 13 nights with the Nanshan One-meter Wide-field Telescope. We have detected 88 variable stars, containing 72 new variable stars and 16 known variable stars. By analyzing these light curves, we classified the variable stars as follows: 26 eclipsing binaries, 52 pulsating stars, four rotating variables, and six unclear type-variable stars for which their periods are much longer than the time baseline chosen. Employing Gaia DR2 parallax, kinematics, and photometry, the cluster memberships of these variable stars were also analyzed for NGC 2355. In addition to the 11 variable members reported by Cantat-Gaudin et al. (2018), we identify four more variable member candidates located at the outer region of NGC 2355 and showed homogeneity in space positions and kinematic properties with the cluster members. The main physical parameters of NGC 2355 estimated from the two-color and color–magnitude diagrams are log(age/yr) = 8.9, E(B − V) = 0.24 mag, and [Fe/H] = −0.07 dex.

New CCD Astrometric Observations of Himalia Using Gaia DR2 in 2015–2021

Abstract The long arc and high-quality astrometric measurements of outer irregular satellites are prerequisites for improving their orbital theories and increasing the precision of their ephemerides. In order to obtain good astrometric positions of Himalia, the largest irregular satellite of Jupiter, we have processed and reduced 911 ground-based CCD frames obtained between 2015 and 2021 by three telescopes (including 1 and 2.4 m telescopes at Yunnan Observatory, and 0.8 m telescope at Purple Mountain Observatory) over 61 nights. Subtracting off the companion star of our target by constructing an effective point-spread function (ePSF) model in some CCD frames, the ePSF-subtracted technique is used to reduce the centering error. Some additional techniques are applied in data reduction to further improve positional accuracy and precision of Himalia. This includes geometric distortion correction, weighted polynomial plate models, and the precision-premium effect, since their relative positional measurements have better precision when two objects are very near (e.g., less than 60″). The star catalog Gaia DR2 is used for astrometric calibration, and theoretical positions of Himalia are retrieved from JPL Horizons ephemeris, including the satellite ephemeris Jup344 and the newest planetary ephemeris DE441. Our results show the mean (O − C)s (observed minus computed) of the positional residuals of Himalia are −0."004 and 0.″005 in R.A. and decl., respectively, and their corresponding standard deviations are about 0.″020 in each direction.

Variable stars in the 50BiN open cluster survey. II. NGC 869

This work presents a time-series photometric variability survey of the young open cluster NGC 869. More than 13 000 CCD frames in the BV filters were collected on 19 nights between 2014 November 6 and 2014 December 24. In a 20′ × 20′ field centered on the cluster, we detected a total of 28 stars showing photometric variability, 12 of which are new discoveries. The classifications and memberships of the variable stars are discussed according to the behaviors and periods of the light curves as well as their positions on the H-R diagram. These results conclude that 22 variable stars are probable members of the cluster while six other stars belong to the field star population. They are categorized as 18 pulsating variable stars (four β Cep, seven SPB, one β Cep / SPB, four Be stars, and two δ Sct / γ Dor candidates), seven eclipsing binaries (five EA and two EB) and three unknown type stars.

Investigation and application of fitting models for centering algorithms in astrometry

To determine the precise positions of stars in CCD frames, various centering algorithms have been proposed for astrometry. The effective point spread function (ePSF) and the Gaussian centering algorithms are two representative centering algorithms. This paper compares in detail and investigates these two centering algorithms in performing data reduction. Specifically, synthetic star images in different conditions (i.e. profiles, fluxes, backgrounds and full width at half maximums) are generated and processed. We find that the difference in precision between the two algorithms is related to the profiles of the star images. Therefore, the precision comparison results using an ideal Gaussian-profile star image cannot be extended to other more specific experimental scenarios. Based on the simulation results, the most appropriate algorithm can be selected according to the image characteristics of observations, and the loss of precision of other algorithms can be estimated. The conclusions are verified using observations captured by the 1-m and 2.4-m telescopes at Yunnan Observatory.

Investigating variable stars in the open cluster NGC 1912 and its surrounding field

In this work, we studied the variable stars in the open cluster NGC 1912 based on the photometric observations and Gaia DR2 data. More than 3600 CCD frames in B, V, R filters were reduced, and we obtained the light curves that span about 63 hours. By analyzing these light curves, we detected 24 variable stars, including 16 periodic variable stars, seven eclipsing binaries and one star whose type is unclear. Among these 24 variable stars, 11 are newly discovered, which are classified as six γ Doradus stars, one δ Scuti star, three detached binaries and one contact binary. We also confirmed 13 previously known variable stars. Based on cluster members identified by Cantat-Gaudin et al. (), we inferred cluster memberships for these detected variable stars. Using Gaia DR2 data, we plotted a new color-magnitude diagram for NGC 1912, and showed the nature of variable cluster members in kinematical properties and heliocentric distance. Among the 24 variable stars, seven variables are probable cluster members, which show homogeneity in kinematic characters and space position with the established cluster members. Four of the seven variable cluster members are the previously discovered stars, consisting of two γ Dor stars and two δ Sct stars. The remaining three variable cluster members, which are all γ Dor stars, are firstly detected in this work. The main physical parameters of these variable cluster members estimated from the color-magnitude diagram are log(age/yr) = 8.75, [Fe/H] = –0.1, m – M = 10.03 mag, and E(B – V) = 0.307.

Investigating variable stars in the open cluster NGC 1912 and its surrounding field

In this work, we studied the variable stars in the open cluster NGC 1912 based on the photometric observations and $Gaia$ DR2 data. More than 3600 CCD frames in B, V, R filters were reduced, and we obtained the light curves that span about 63 hours. By analyzing these light curves, we detected 24 variable stars, including 16 periodic variable stars, seven eclipsing binaries and one star whose type is unclear. Among these 24 variable stars, 11 are newly-discovered, which are classified as six gamma Doradus stars, one delta Scuti star, three detached binaries and one contact binaries. We also confirmed 13 previously known variable stars. Based on cluster members identified by Cantat-Gaudin et al. (2018), we inferred cluster memberships for these detected variable stars. Using Gaia DR2 data, we plotted a new color-magnitude diagram for NGC 1912, and showed the nature of variable cluster members in kinematical properties and heliocentric distance. Among the 24 variable stars, seven variables are probable cluster members, which show homogeneity in kinematic characters and space position with the established cluster members. Four of the seven variable cluster members are the previously discovered stars, consisting of two gamma Dor stars and two delta Sct stars. The remaining three variable cluster members, which are all gamma Dor stars, are firstly detected in this work. The main physical parameters of these variable cluster members estimated from the color-magnitude diagram are log(age/yr)=8.75, [Fe/H]=-0.1, m-M=10.03 mag, and E(B-V)=0.307.

Astrometric Membership Tests for the Zinn–Newell–Gibson UV-bright Stars in Galactic Globular Clusters

Abstract In 1972, Zinn, Newell, & Gibson (ZNG) published a list of 156 candidate UV-bright stars they had found in 27 Galactic globular clusters (GCs), based on photographs in the U and V bands. UV-bright stars lie above the horizontal branch (HB) and blueward of the asymptotic giant branch (AGB) and red giant branch in the clusters’ color–magnitude diagrams. They are in rapid evolutionary phases—if they are members and not unrelated bright foreground stars. The ZNG list has inspired numerous follow-up studies, aimed at understanding late stages of stellar evolution. However, the ZNG candidates were presented only in finding charts, and celestial coordinates were not given. Using my own collection of CCD frames in u and V, I have identified all of the ZNG objects, and have assembled their coordinates, parallaxes, and proper motions from the recent Gaia Early Data Release 3 (EDR3). Based on the Gaia astrometry, I have determined which objects are probable cluster members (45% of the sample). For the members, using photometry from EDR3, I have assigned the stars to various evolutionary stages, including luminous post-AGB stars, and stars above the HB. I point out several ZNG stars of special interest that have still, to my knowledge, never been studied in detail. This study is an adjunct to a forthcoming survey of the Galactic GCs in the uBVI photometric system, designed for detection of low-gravity stars with large Balmer discontinuities.

Using Gaia DR2 to solve differential colour refraction and charge transfer efficiency issues

ABSTRACT The Gaia DR2 catalogue released in 2018 gives information about more than one billion stars, including their extremely precise positions that are not affected by the atmosphere, as well as the magnitudes in the G, RP, and BP passbands. This information provides great potential for the improvement of the ground-based astrometry. Based on Gaia DR2, we present a convenient method to calibrate the differential colour refraction (DCR). This method only requires observations with dozens of stars taken through a selected filter. Applying this method to the reduction of observations captured through different filters by the 1- and 2.4-m telescopes at Yunnan Observatory, the results show that the mean of the residuals between observed and computed positions (O − C) after DCR correction is significantly reduced. For our observations taken through an N (null) filter, the median of the mean (O − C) for well-exposed stars (about 15 G-mag) decreases from 19 to 3 mas, thus achieving better accuracy, i.e. mean (O − C). Another issue correlated is a systematic error caused by the poor charge transfer efficiency (CTE) when a CCD frame is read out. This systematic error is significant for some of the observations captured by the 1-m telescope at Yunnan Observatory. Using a sigmoidal function to fit and correct the mean (O − C), a systematic error up to 30 mas can be eliminated.

COMPARISSON OF THE RESULTS OF PROCESSING OF CCD OBSERVATIONS OF SELECTED OPEN CLUSTERS

Observations of open clusters at the Re- search Institute “Mykolaiv Astronomical Observatory” (RI MAO) were performed using the KT-50 telescope (D=500mm, F=3000mm) in 2011 – 2018. As the light re- ceiver, a CCD camera Apogee Alta U9000 (3K x 3K, FOV 42.6' x 42.6') in short drift scan mode was used. In short drift scan mode each observation consisted of several CCD frames with partial overlap in right ascension. All observa- tions were performed using R light filter. The exposure time was 20 seconds for all frames. All previous astromet- ric processing was carried out by the Astrometrica program and UCAC4 reference catalog. Using this data we received two catalogs of positions of 4.2 million stars (J2013.6) and 3.3 million starts (J2017.3) in the vicinity of open clusters with accuracy (0.03-0.07). Unfortunately, current version of Astrometrica program have problem with data reduction with Gaia reference catalog in areas with big star density, like vicinity of open clusters near the plane of the Galaxy. At this article, we compared our old results with the new one for several open clusters which carried out with the author's set of programs with primary processing in the MIDAS environment. As reference stars the Tycho2, UCAC4 and Gaia DR2 catalogs were used. The reduction of 548 frames was performed using a polynomial of the third degree. The results obtained by author programs with reference catalogs UCAC4 and Gaia, showed good con- vergence. Several catalogs of positions of stars up to 17.5 m was obtained. The accuracy of the catalogs is σ RA =0.027 and σ Dec =0.033 for Gaia reference catalog and σ RA =0.032 and σ Dec =0.036 for UCAC4 reference catalog. At the same time, the accuracy of intraframe processing with the Gaia reference catalog turned out to be near 2 times better than the analogous one with the UCAC4 catalog. The compari- son showed the possibility of receiving more good results with Gaia reference catalog.

CCD Observations and Period Change of the Type ab RR Lyrae Star DV Mon

We took a total of 635 B-, V-, and Ic-band CCD frames for the RRab Lyr type variable DVMon, which has a close bright visual companion with a separation of about 1.9′. Observations were made with the 76-cm telescope of the South African Astronomical Observatory (SAAO, South Africa) using SBIG CCD ST-10XME. For the first time, we obtained reliable separate PSF-photometry of both stars and determined their coordinates. We used all available data to construct the O — C diagram spanning a 110-year long time interval, which allowed us to reveal at least three sudden changes of the pulsation period around JD 2438000, 2453500, and 2456500. Our high resolution echelle spectra with the Southern African Large Telescope (SALT) showed that DV Mon belongs to type ab RR Lyrae variables of the Galactic thick disk.

New CCD astrometric observations of the five major uranian satellites using Gaia DR1 in 2014–2016

710 CCD frames, observed by 1–m telescope at Yunnan Observatory over 15 nights, have been reduced to derive new precise positions of the five Uranian major satellites (Ariel, Umbriel, Titania, Oberon and Miranda). In the pixel positional measurement of the faint satellites near Uranus, a halo removal procedure similar to that of Veiga et al. (Veiga and Vieira Martins, 1995) was carried out. After that we adopted a two-dimensional symmetric Gaussian model with as high as a third order polynomial to deliver the pixel positions of the concerned satellites. Lastly, the positions of satellites were measured with reference stars from Gaia DR1. The theoretical positions of Uranian satellites were retrieved from the Jet Propulsion Laboratory (JPL) Horizons System that includes the satellite ephemeris ura111, while the position of Uranus was from DE431. We also compared our observations with different satellite ephemerides from the Institut de Mcanique Cleste et de Calcul des phmrides (IMCCE). When Gaia DR1 is used for the reference star catalogue and meanwhile satellites ephemeris is obtained from JPL, our results show that the absolute values of the mean (O-C) (observed minus computed) residuals are not greater than 0.020 arcsec in both right ascension and declination for the five satellites. The positional precision is better than 0.030 arcsec for the four greatest Uranian satellites and 0.050 arcsec for Miranda in each direction.

ANALYSIS OF MASS CCD OBSERVATIONS TO IMPROVE THE ACCURACY OF ASTROMETRIC PROCESSING

In Research Institute: Mykolaiv Astronomical Observatory (RI MAO) regularly observations of fields with open clusters on the KT50 telescope (D = 500 mm, F = 3000 mm) with an Alta U9000 CCD camera (3k × 3k, FOV 42.6' × 42.6') in drift scan mode are carried out. For this observation mode, we investigated the dependence of the differences between observed minus calculated (O-C) angular coordinates of reference stars in depending on X coordinate (direction perpendicular to the direction of charge transfer) in the CCD coordinate system. The data of observations of open clusters obtained in the RI MAO in 2011-2017 were used for the study. The data array used to obtain the distribution (O-C) for right ascension (RA) and declination (DEC), depending on X, contains 62 million single observations of stars. The processing of the original data was carried out using the Astrometrica program with the reference catalogue UCAC4. The distribution of the (O-C) value as a function of X according to RA and DEC was obtained by the method of least squares. For the solution is a 10th-degree polynomial of X and a third degree from the integral intensity of the object in the image was used. The study showed the presence of significant (0.01-0.02) systematic errors in the field of the matrix for bright stars (10-12) m . For faint stars, the amplitude of the constant part decreases significantly while maintaining the periodic component. Similar studies have also been carried out for a lot of CCD frames obtained from astronomical databases for other instruments. The results will be used to improve the accuracy of astrometric catalogues obtained with the KT50 telescope and to improve the accuracy of the proper motions of stars in the vicinity of open clusters.

Automatic detection of recoil-proton tracks and background rejection criteria in liquid scintillator-micro-capillary-array fast neutron spectrometer

We describe an analysis procedure for automatic unambiguous detection of fast-neutron-induced recoil proton tracks in a micro-capillary array filled with organic liquid scintillator. The detector is viewed by an intensified CCD camera. This imaging neutron detector possesses the capability to perform high position-resolution (few tens of μm), energy-dispersive transmission-imaging using ns-pulsed beams. However, when operated with CW or DC beams, it also features medium-quality spectroscopic capabilities for incident neutrons in the energy range 2–20 MeV.In addition to the recoil proton events which display a continuous extended track structure, the raw images exhibit complex ion-tracks from nuclear interactions of fast-neutrons in the scintillator, capillaries quartz-matrix and CCD. Moreover, as expected, one also observes a multitude of isolated scintillation spots of varying intensity (henceforth denoted ”blobs”) that originate from several different sources, such as: fragmented proton tracks, gamma-rays, heavy-ion reactions as well as events and noise that occur in the image-intensifier and CCD. In order to identify the continuous-track recoil proton events and distinguish them from all these background events, a rapid, computerized and automatic track-recognition-procedure was developed.Based on an appropriately weighted analysis of track parameters such as: length, width, area and overall light intensity, the method is capable of distinguishing a single continuous-track recoil proton from typically surrounding several thousands of background events that are found in each CCD frame.