An Analysis of the Fragmentation of Observing Time At the Muztagh-Ata Site

Cloud cover plays a pivotal role in assessing observational conditions for astronomical site-testing.Except for the fraction of observing time,its fragmentation also wields a significant influence on the quality of nighttime sky clarity.In this article,we introduce the functionΓ∈[0,1],designed to comprehensively capture both the fraction of available observing time and its continuity.Leveraging in situ measurement data gathered at the Muztagh-Ata site between 2017 and 2021,we showcase the effectiveness of our approach.The statistical result illustrates that the Muztagh-Ata site affords approximately 122 nights that were absolutely clear and 205 very good nights annually,corresponding toΓ≥0.9 andΓ≥0.36 respectively.

Site-testing at the Muztagh-ata Site V.Nighttime Cloud Amount during the Last Five Years

The clarity of nights is the major factor that should be carefully considered for optical/infrared astronomical observatories in site-testing campaigns.Cloud coverage is directly related to the amount of time available for scientific observations at observatories.In this article,we report on the results of detailed night-time cloud statistics and continuous observing time derived from ground-based all-sky cameras(ASCs)at the Muztagh-ata site from 2017to 2021.Results obtained from acquisition data show that the proportion of the annual observing time at the Muztagh-ata site is 65%,and the best period with the least cloud coverage and longer continuous observing time is from September to February.We made a comparison of the monthly mean observing nights obtained from our ASC and CLARA data set,and results show that the discrepancy between them may depend on the cloud top heights.On average,this site can provide 175 clear nights and 169 nights with at least 4 hr of continuous observing time per year.

Upgraded photometric system on the 85-cm telescope at Xinglong station

The 85-cm telescope at Xinglong station is a prime focus system that operates well with high science outputs. The telescope has been upgraded since 2014 with a new corrector, and new filters and camera, which are provided by Beijing Normal University. The filter set is the Johnson-Cousins UBV RI system. We report the test results of the new system including bias, dark current, linearity, gain and readout noise of the CCD camera. Then we derive accurate instrumental calibration coefficients in UBV RI bands with Landolt standard stars during photometric nights. Finally, we give the limiting magnitudes with various exposure times and signal-to-noise ratios for observers as references.

Site-testing at Muztagh-ata site Ⅰ:ground meteorology and sky brightness

Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions,one of the associated basic tasks.As one of three potential sites to host the 12-meter Large Optical/infrared Telescope(LOT),the Muztagh-ata site,which is located on the Pamir Plateau in Xinjiang,in west China,began its site-testing task in the spring of 2017.In this paper,we firstly start with an introduction to the site and then present a statistical analysis of the ground-level meteorological properties such as air temperature,barometric pressure,relative humidity,and wind speed and direction,recorded by an automatic weather station with standard meteorological sensors for a two-year duration.We also show the monitoring results of sky brightness during this period.

Site-testing at Muztagh-ata site Ⅲ:temperature inversion in surface-layer atmosphere

In this article,we present detailed seasonal,monthly and daily statistics of temperature difference in the surface layer at the Muztagh-ata site based on the temperature measurements at two heights of 2 m and6 m.We find that temperature inversion occurs frequently at our site during nighttime,especially during the cold season.Strong temperature inversion always represents stable atmospheric turbulence,which is crucial for an optical observatory.By analyzing the behavior of temperature inversion and its correlation with wind and cloud amount,one conclusion can be made that radiation inversion is the main reason for the existence of temperature inversion in the surface-layer at the Muztagh-ata site.

Site testing campaign for the Large Optical/infrared Telescope of China:overview

The Large Optical/infrared Telescope(LOT)is a ground-based 12 m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade.Based on satellite remote sensing data,along with geographical,logistical and political considerations,three candidate sites were chosen for ground-based astronomical performance monitoring.These sites include:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.Up until now,all three sites have continuously collected data for two years.In this paper,we will introduce this site testing campaign,and present its monitoring results obtained during the period between March 2017 and March 2019.

The wide-field photometric system of the Nanshan One-meter Telescope

The Nanshan One-meter Wide-field Telescope is a prime focus system that is located at Nanshan Station of Xinjiang Astronomical Observatories.The field of view was designed to 1.5°× 1.5°,and the Johnson-Cousins UBVRI system was chosen as the main filter set.The telescope has been providing observation services for astronomers since September 2013.Variable source searching and time-domain surveys are the main scientific goals.The system’s test results are reported including linearity,dark current,bias,readout noise and gain of the CCD camera.The accurate instrumental calibration coefficients in UBVRI bands were driven with Landolt standard stars during photometric nights.Finally,the limiting magnitudes are given with signal-to-noise ratios and various exposure times for observers.

Site testing at Muztagh-ata site Ⅱ:seeing statistics

In this article,we present a detailed analysis of the statistical properties of seeing for the Muztaghata site which is a candidate site for hosting the future Chinese Large Optical/infrared Telescope(LOT)project.The measurements were obtained with differential image motion monitors(DIMMs)from April2017 to November 2018 at different heights during different periods.The median seeings at 11 m and6 m are very close but significantly different from that on the ground.We mainly analyzed the seeing at11 m monthly and hourly,having found that the best season for observing was from late autumn to early winter and seeing tended to improve during the night only in autumn.The analysis of the dependence on temperature inversion,wind speed and direction also was made and the best meteorological conditions for seeing are given.

Long-term analysis of clear nights using satellite data considering astronomical sites in western China

A large ground-based optical/infrared telescope is being planned for a world-class astronomical site in China.The cloud-free night percentage is the primary meteorological consideration for evaluating candidate sites.The data from GMS and NOAA satellites and the MODIS instrument were utilized in this research,covering the period from 1996 to 2015.Our data analysis benefits from overlapping results from different independent teams as well as a uniform analysis of selected sites using GMS+NOAA data.Although significant ground-based monitoring is needed to validate these findings,we identify three different geographical regions with a high percentage of cloud-free conditions(~83%on average),which is slightly lower than at Mauna Kea and Cerro Armazones(~85%on average)and were chosen for the large international projects TMT and ELT respectively.Our study finds evidence that cloud distributions and the seasonal changes affected by the prevailing westerly winds and summer monsoons reduce the cloud cover in areas influenced by the westerlies.This is consistent with the expectations from climate change models and is suggestive that most of the identified sites will have reduced cloud cover in the future.

Data processing and data products from 2017 to 2019 campaign of astronomical site testing at Ali,Daocheng and Muztagh-ata

Based on previous site testing and satellite cloud data,Ali,Daocheng and Muztagh-ata have been selected as candidate sites for the Large Optical/Infrared Telescope(LOT) in China.We present the data collection,processing,management and quality analysis for our site testing based on using similar hardware.We analyze meteorological data,seeing,background light,cloud and precipitable water vapor data from 2017 March 10 to 2019 March 10.We also investigated the relative usefulness of our all-sky camera data in comparison to that from the meteorological TERRA satellite data based on a night-by-night comparison of the correlation and consistency between them.We find a 6% discrepancy arising from a wide range of factors.

Pulsations of the High-Amplitude δ Scuti star YZ Bootis

We present a study on pulsations of the high-amplitudeδScuti star YZ Boo based on photometric observations in Johnson V and R bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory（XAO）and the Xinglong 85-cm telescope of National Astronomical Observatories,Chinese Academy of Sciences（NAOC）.Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics,with the fourth and fifth being newly detected.Thirtynine new times of maximum light are determined from the light curves,and combined with those in the literature,we construct the O-C diagram,derive a new ephemeris and determine a new value for the updated period of 0.104091579（2）.In addition,the O-C diagram reveals an increasing rate of period change for YZ Boo.Theoretical models are calculated and constrained with the observationally determined parameters of YZ Boo.The mass and age of YZ Boo are hence derived as M=1.61±0.05 M_⊙ and age=（1.44±0.14）×10~9 yr,respectively.With both the frequency of the fundamental radial mode and the rate of period change,YZ Boo is located at the post main sequence stage.

KIC 10417986:Spectroscopic Confirmation of the Nature of the Binary System with aδScuti Component

KIC 10417986 is a short orbital period(0.0737 day)ellipsoidal variable star with aδSct andγDor hybrid pulsation component discovered by Kepler.The ground-based spectroscopic observations were carried out in the winters of 2020 and 2021 to investigate the binary nature of this star.We derive the orbital parameters using the rvfit code with a result of K_(1)=29.7±1.5 km s^(-1),γ=-18.7±1.7 km s^(-1),and confirm an orbital period of 0.84495 day instead of the result given by Kepler.The atmospheric parameters of the primary are determined by the synthetic spectral fitting technique with the estimated values of T_(eff)=7411±187 K,log g=4.2±0.3 dex,[M/H]=0.08±0.09 dex and vsini=52±11 km s^(-1).KIC 10417986 is a circular orbit binary system.From the single-lined nature and mass function of the star,the derived orbital inclination is 26°±6°,and the mass of the secondary is 0.52_(-0.09)^(+0.18)M_(⊙),which should be a late-K to early-M type star.Fourteen frequencies are extracted from Kepler light curves,of which six independent frequencies in the high-frequency region are identified as the p-mode pulsations ofδSct star,and one independent frequency in the low-frequency region(f_(2)=1.3033 cd^(-1))is probably the rotational frequency due to the starspots rather than the ellipsoidal effect.