The current development of the Taiwan Meteor Detector System (TMDS) with a dedication to the Geminids 2017 and 2018

Journal Pre-proof The current development of the Taiwan Meteor Detector System (TMDS) with a dedication to the Geminids 2017 and 2018 Zhong-Yi Lin, Hsin-Chang Chi, Bo-Hao Wang, Zong-Yi Lin, Chih-Cheng Liu, Jim Lee, Hung-Chin Lin, Bingsyun Wu, Xue-Hui Ma, Chia-Hsien Liao PII:

S0032-0633(18)30273-3

DOI:

https://doi.org/10.1016/j.pss.2019.104763

Reference:

PSS 104763

To appear in:

Planetary and Space Science

Received Date: 31 July 2018 Revised Date:

20 September 2019

Accepted Date: 29 September 2019

Please cite this article as: Lin, Z.-Y., Chi, H.-C., Wang, B.-H., Lin, Z.-Y., Liu, C.-C., Lee, J., Lin, H.-C., Wu, B., Ma, X.-H., Liao, C.-H., The current development of the Taiwan Meteor Detector System (TMDS) with a dedication to the Geminids 2017 and 2018, Planetary and Space Science (2019), doi: https:// doi.org/10.1016/j.pss.2019.104763. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier Ltd. All rights reserved.

The Current Development of The Taiwan Meteor Detector System (TMDS) with a dedication to the Geminids 2017 and 2018 Zhong-Yi Lin Institute of Astronomy, NCU, No. 300, Zhongda Rd., Zhongli Dist., Taoyuan City 32001, Taiwan

Hsin-Chang Chi Department of Physics, NDHU, No. 1, Sec. 2, Da Hsueh Rd. Shoufeng, Hualien 97401, Taiwan

Bo-Hao Wang Department of Applied Mathematics, NDHU, No. 1, Sec. 2, Da Hsueh Rd. Shoufeng, Hualien 97401, Taiwan

Zong-Yi Lin Department of Physics, NDHU, No. 1, Sec. 2, Da Hsueh Rd. Shoufeng, Hualien 97401, Taiwan

Chih-Cheng Liu Department of Applied Mathematics, NDHU, No. 1, Sec. 2, Da Hsueh Rd. Shoufeng, Hualien 97401, Taiwan

Jim Lee Taipei Astronomical Museum, Taipei, Taiwan

Hung-Chin Lin Institute of Astronomy, NCU, No. 300, Zhongda Rd., Zhongli Dist., Taoyuan City 32001, Taiwan

Bingsyun Wu Taichung municipal Hui-Wen high school, Taichung, Taiwan

Xue-Hui Ma, Chia-Hsien Liao Ken-Ting Observatory, NTU, Taiwan

Email addresses: [email protected] (Zhong-Yi Lin), [email protected] (Hsin-Chang Chi)

Preprint submitted to Planetary and Space Science

October 7, 2019

Abstract We summarize the outcomes of the first 2-year period observations using the Taiwan Meteor Detector System (TMDS) since its establishment in August 2016. The TDMS is an automated four-station video meteor system equipped to record meteors as well as obtain the meteor orientations in space. The multistation observations of an individual meteor make feasible determination of the orbital parameters corresponding to the meteor. The associated parent bodies of individual meteors are consequently identified from the orbital information. To demonstrate, we also present an analysis of the results from the Geminid meteor stream in 2017 and 2018 with the magnitude and velocity distribution being provided. In addition, a conclusive interrelation is verified while applying the Southworth-Hawkins D-criterion (Dsh ) to compare the similarities between Geminids and the asteroid 3200 Phaethon orbits. The newly established TMDS can perform real-time as well as long-term synchronous surveillance of meteor events. Keywords: Geminids, orbits, (3200) Phaethon

1. Introduction A meteor occurs when a meteoroid (comet debris or asteroid fragment) strikes Earth’s atmosphere at high speeds. Active combustions, which leads to evaporation of the meteoroid in the atmosphere, generally occur due to the 5

instantaneous compressions of the air confronting a meteoroid. Such a scenario usually displays a familiar white ”shooting star” to show up in the sky. In fact, every year, 30000 tons of interplanetary dust fall in the Earth’s atmosphere. Studying meteors and meteoroids can provide a clue about their parent objects: comets (Trigo-Rodriguez et al., 2009)[1] and asteroids (Porubcan et al.,

10

2004)[2]. The strength of the meteoroids, for instance, provides information as to the structure and evolution of the parent body. Through meteor studies, the relation between the properties of comets and asteroids can be further investi2

gated. Studying meteors also gives us a better understanding of the near Earth environment, and detail information on the dynamical, physical and chemical 15

properties of comets, asteroids and their evolution in the solar system (Prakash et al. 2009)[3].

Motion activated video recording is one of the most convenient detection techniques for meteor observations. Under the collaboration among three insti20

tutions: the Graduate Institute of Astronomy at National Central University (NCU), the Department of Physics at National Dong-Hua University (NDHU), and the Taipei Astronomical Museum (TAM), the Taiwan Meteor Detector System (TMDS) is founded and started operations in late-July of 2016. The TDMS, to accompany with other meteor observing systems around the world, is aim-

25

ing at the determination of the physical properties of meteoroids. Particular attention of the TDMS is paid to improve the understanding of poorly studied showers and their associated parent bodies. As is well known, the International Astronomical Union’s Meteor Data Center has accomplished a catalog to list 957 proposed showers, in which 112 meteor showers are certain to exist. Never-

30

theless, in fact, only 32 of the 112 existing meteor showers are associated with identified parent bodies. The Geminids is one of the largest showers belonging to the catalogued meteor database; especially, it has been studied using various observation techniques by plenty of researchers over a long time. For example, a comprehensive review of observational and theoretical studies of the Geminid

35

stream has been presented by Neslusan (2015)[4]. Moreover, using video technique, several authors have reported observations on the Geminid meteor shower in the recent past. Among them, there are Ueda & Fujiwara (1993)[5]; de Lignie et al. (1993); Elliott et al. (1993)[6]; Andreic & Segon (2008)[7]; Jenniskens et al. (2010, 2011, 2016)[8][9][10]; Trigo-Rodriguez et al. (2010)[11]; Toth et al.

40

(2011, 2012)[12]; Rudawska et al. (2013)[13];Madiedo et al. (2013)[14]; Molau et al. (2015, 2016)[15][16], Hajdukova et al. (2017)[17], etc.

In the following paragraphs, we introduce, in Sec. 2, the TMDS along with 3

Table 1: Location of TMDS observing sites.

Latitude◦ (N)

Longitude◦ (E)

Altitude (m)

In (year/moth)

Lulin (E1)

120.8736

23.5833

2862

2016/7- present

Lulin (S1,N1)

120.8736

23.5833

2862

2017/12 -present

Hutain

121.5420

25.1700

660

2016/8 -2018/12

KTO

120.6982

22.0500

38.4

2017/11 -present

121.2424

23.2345

2500

2018/5 -present

Sation

Fushoushan FSS (E,S)

several examples, which demonstrate the capabilities of the system. In Sec. 3, 45

we present the statistical outcomes and analyses of the data sets acquired by the TDMS from its startup in 2016 to end of 2018. Preliminary results from the observations of the Geminids meteor shower 2017 and 2018 are given in Sec. 4. Furthermore, Sec. 5 is devoted to discussion and summary.

2. Instrumentation and data analysis 50

Since its start into operation in August 2016, the TDMS routinely monitors the sky to search for luminous near-earth objects, especially meteors. With the intention to record as many meteors as possible by adopting a multi-station configuration, the TMDS consists of ten cameras distributed at four different locations in Taiwan at present (Mt. Yangmingshan, Fushoushan Farm, Lulin

55

Observatory, and Kenting Observatory, see Figure 1). The geographic coordinates of the four sites are listed in Table 1. For obtaining better precision determinations of a meteor trajectory, the four observing stations are located between 93.6 km and 250.7 km apart. The hardware facilities for observations and software programs for data analysis are described below in detail.

60

2.1. System specifications Individual observation stations of the TDMS use Watec or Starlight cameras for data recordings. The limiting magnitudes and fields of view of the cameras

4

Figure 1: The locations of the 4 observing stations currently affiliated with the Taiwan Meteor Detection System (TMDS). From northern to southern Taiwan, the locations of the 4 installed stations are at Hutain elementary school inside Yang-Ming-Shan National Park, Fushoushan Farm, Lulin observatory, and Kenting observatory, respectively.

5

Table 2: System specifications

Stations

Cameras

Lulin E1

Lulin S1

Lulin N1

Hutain

E1

S1

N1

Hutain

902H2U

902H2U

910HX

902H2U

KTO

STARLIGHT

FSS (S)

FSS (E)

S

E

902H2U

902H2U

EX27 Maglimit

3.0

3.6

6.3

1.9

3.4

3.2

3.3

FOV

69.5

88.9

28.3

64.7

64.6

69.6

58.3

are listed in Table 2. The data recordings are sampled at a rate 33 FPS (frame per second), which corresponds to an approximately 0.03s resolution of each 65

frame. Besides, timing information is calibrated from invoking the Network Time Protocol (NTP) services supported by the U.S. government. Instead of simply correcting the system clock times periodically, NTP responds to adjust the clock rates of local systems to ensure the clock is always accurate to better than one frame time.

70

2.2. Software and data analysis The present TDMS employs the UFO Capture software version 4.272 (SonotaCo 2009)[18] for video recordings of meteor events. The UFO Capture tool set consists of 3 sub-packages; UFO Capture, UFO Analyser and UFO Orbit. Here, we give a brief outline of the sub-packages as follows: First, the UFO Cap-

75

ture is designed to accomplish motion-activated detections. Second, the UFO Analyser performs classifications of detected motional objects based on features in brightness, size and duration, respectively. In addition, it best conforms the sky video-snapshot to a standard star map under superimposition; parameters for astrometry and photometry are estimated. Third, the UFO Orbit is im-

80

plemented for determining meteor orbits by analyzing data sets acquired from simultaneous multi-station detections. Since no automatic reduction or calculation software is applicable for filtering detected events at present, significant data sets are reduced from manual examinations of the raw database periodically. Confirmed meteor events are further 6

Figure 2: On September 22, 2016, two Meteor Cameras being operated 200 km apart mutually captured a common meteor.

85

analyzed using the UFO software package, which generates uniformly formatted data loggings suitable for compilations in spite of a vast detection acquired from distinct stations.

3. Results and analyses From August 2016 to December 2018, successive operations of the TDMS 90

have registered about twenty thousand meteor trails. Among the detected trails, only about 7% (see Fig. 2) are successfully providing definite orbit information. This deficiency in achieving meteor orbits is attributable to the relatively unfavorable weather conditions around the observing stations Hutain, KTO and the most recently installed Fushoushan (FSS). It is initially anticipated that the

95

Fushoushan station should operate as efficient as the Lulin observatory since the geographical conditions are comparable. However, the actual situation is not so because of several uncertain weather factors. Table 3 shows the accumulated detections in each station whereas table 4 gives the meteor orbits determined using multi-station orientations of a meteor captured by at least 2 individual

100

stations. Since FSS was online just a few months, the number of the meteor orbits has been increasing dramatically in late 2018. The reason might be due to the relatively good weather condition compared to Hutain and KTO.

7

Table 3: The accumulated detections in Taiwan Meteor Detection System (TMDS) from July 2016 to December 2018

Sation (direction) Events

Lulin

Hutain

KTO

FSS

(E.N.S)

(SE)

(NE)

(E.S)

17978

886

821

926

Table 4: The orbits in Taiwan Meteor Detection System (TMDS) from August 2017 to December 2018

Stations

Orbits

Lulin

Hutain

KTO

FSS (S)

FSS (E)

FSS (E)

Hutain

KTO

Lulin

KTO

Lulin

KTO

105

11

263

46

311

18

The knowledge of the meteor magnitudes is an important and complicated subject deserving advanced studies. Factors affecting the magnitudes include 105

meteor velocity, height, compositions, size, mass, et cetera. In addition, atmospheric conditions also play an influential role. We use an empirical formula to analyze the event distributions depending on magnitudes. The prescription is given as the following

N (m) =

A(mc − m)2 . eB(mc −m) − 1

(1)

where mc is the detection magnitude cutoffs (Maglimit ) specified by a cam110

era, m is meteor magnitude, and N(m) represents the amount of meteor events depending on magnitude m. The parameters A and B, obtained from optimization processes to best fit the raw-data distributions, describe the characteristics of the magnitude distributions. The apparent magnitude cutoffs for cameras installed at individual stations are given in Table 2 with regard to the sensitiv-

115

ities of corresponding cameras. We have applied the above empirical formula to analyze the magnitude distribution of full-calibrated meteor events captured from late 2016 to 2018. Figure 3 presents the results from our analyses. Because of the detecting restrictions on magnitude, the faintest meteors to be detectable are, for example, with magnitudes around +2 at Hutain and +7 at Lulin N1B.

8

Figure 3: Histogram comparing the magnitude distribution of the detected meteor events at Lulin observatory (E1, N1, and S1), KTO, Hutain in left-panel and FSS (E, and S) in right-panel respectively, between 2016 and 2018. For a few of them, the magnitude can not be determined due to readout noise from the recorded files. The deviations among different stations are owing to several factors: the start-up time, camera sensitivity, weather condition, and so on.

120

As it is shown in Figure 3, positions of the high-magnitude ends of the magnitude distributions are consistently put by the limits of camera detecting capabilities. The computations of orbits are mainly performed using the UFOOrbit software. UFOOrbit allows multiple parameter settings. Our database accommodates all the unfiltered data obtained by setting Q0. Commonly detected

125

meteors are assumed when the occurrences of a monitored meteor differ with an interval shorter than 3 seconds. The Q0 parameter provides all possible combinations, and the interval of dt = 3s is pre-chosen to account for 2 inevitable causes: The first arises from the difficulty to synchronize precisely the multistation time settings. The second is, depending on the camera sensitivities,

130

the desynchronized triggers of event recordings at distinct observation stations. Positions and velocities of simultaneously detected meteors from multi-stations are calculated subsequently by applying the triangulation method. Practical properness of using the pre-set dt=3s is justified since very few false-detections of concurrent meteor events are found from operations. To proceed further, with

135

the position and velocity components of individual meteors, the meteor orbits are determined. To sum up, there are 676 orbits identified from two or three 9

Table 5: The classified meteor showers detected using the TMDS from August 2017 to 2018.

Meteor Showers

Active Period

Max (Date)

Orbit Amount

J5etA (Eta Aquarids)

Apr 21- May 12

May 5 ∼6

11

J5sdA (South Delta Aquarids)

Jul 12 - Aug 19

July 28

12

J5Eri (Eta Eridanids)

Aug 3 - Aug 14

Aug 9

4

J5Per (Perseids)

Jul 23 - Aug 22

Aug 12 ∼13

58

J5sPe (September Perseids)

Sep 5 - Sep 21

Sep 9

3

J5Ori (Orionids))

Oct 15 - Oct 29

Oct 21

25

J5sTa (Southern Taurids)

Sep 17 - Nov 27

Oct 30 ∼ Nov 7

15

J5nTa (North. Taurids)

Oct 12 - Dec 2

Nov 4 ∼ 7

11

J5Leo (Leonids)

Nov 13 - Nov 20

Nov 17 ∼ 18

14

J5noO (Nov. Orionids)

Nov 13 - Dec. 6

Nov 28

5

J5Hyd (Sigma Hydrids)

Dec 3 - Dec 15

Dec 12

11

J5Gem (Geminids)

Dec 6 - Dec 19

Dec 13 ∼ 14

53

J5Com (Comae Berenicids)

Dec 8 - Dec 23

Dec 18 - Jan 6

13

separate stations (78 orbits) but only 36% of the meteor orbits can be classified. Table 5 presents the detected 235 orbits with more than one detection in known meteor showers. In other words, about 64% of identified orbits are sporadic or 140

unclassifiable.

4. Observations of the Geminids in 2017 and 2018 The Geminid meteor shower, happening around December 13 and 14, is one of the most familiar and prominent showers, which annually yields a maximum zenith hourly rate over 100. Our observations of the Geminid meteor shower 145

were mainly performed at Lulin, KTO, and FSS stations proceeded for each year December 13 until dawn local time December 15 in 2017 and 2018. Unfortunately, we have only one night data because the adverse weather condition in the island of Taiwan during the 2017 Geminid period. Meanwhile, Hutain station acquired no data of Geminids in 2017 and 2018 because the weather was

10

150

extremely unfavorable even for a single-night observation in Northern Taiwan where the Hutain station is located. Figure 4 summarizes the detected meteors obtained only on the day of December 14 in 2017 and 2018 from these three stations. In 2017, most meteor detections were triggered after midnight because of cirrus cloud in the beginning of night. The observing condition in 2018 was

155

relatively good and then we have more detections of meteor events. To achieve meteoroid orbits, we combined the data obtained from 2 frameworks of pairwise stations, Lulin E1 together with KTO (framework E1+KTO), Lulin S1 along with KTO (framework S1+KTO), Lulin N1 as well as FSS (framework N1+FSS (East and South)) requiring that the video cameras installed are

160

apart farther than ∼100 km to ensure the triangulation method is applicable for determining the trajectory across the Earth’s atmosphere. That trajectory can then be recast into a Heliocentric orbit using prescribed techniques (Ceplecha 1987[19]; Jenniskens et al. 2011[9]). The orbits obtained from the two individual frameworks E1+KTO, N1+ FSS(E), FSS (S) ,and S1+KTO are 53

165

in total. On top of that, the number distribution during the night on December 14 in 2017 and 2018 is shown in Figure 4 as well. In Figure 5, we present the magnitude distribution of these detected orbits in 2017 and 2018. We find that the brightness of the Geminid meteors scatters a wide range from -6 to 0 magnitudes. In general, the size of the meteoroid (comet debris or asteroid

170

fragment) is in scales from mm to cm. The Geminid meteors, on average, are brighter than the meteors of sporadic background or statistics results and this is in accord with previous observations (Evans & Bone 1993)[20]. In Figure 6, we show the event distribution as a function of meteor velocity. More than 74% of Geminids have velocity between 35 and 39 km s−1 . The peak and mean ve-

175

locity are 36.5 and 37.1 km s−1 which is consistent with the IMO (International Meteor Organization) values. In addition to statistics analysis, we employed orbit similarity criteria to justify the interrelated asteroid by using the JPL asteroid orbit database. The Southworth-Hawkins D-criterion (Dsh ) is employed to seek the similarity of two

180

orbits (Southworth & Hawkins, 1963)[21]. A smaller Dsh represents a better 11

Figure 4: The summarized amount of detections from Lulin (East 1, and South 1), KTO and FSS (East and South) stations on December 14, 2017 and 2018.

Figure 5: The magnitude distribution range of Geminids of 53 detections in 2017 and 2018.

12

Figure 6: Velocity distribution for Geminids.

13

Table 6: The results of Dsh criterion with respect to the Phaethon-Geminid complex

Asteroids

Dsh (mean)

Dsh distribution range in 39 orbits

3200 Phaethon

0.087

0.028∼0.146

2005 UD

1.392

1.275∼1.446

1999 YC5

2.801

2.728∼2.843

The elements used for the Dsh criterion estimation of asteroids 3200 Phaethon, 2005 UD, and 1999 YC5 are from JPL small body database.

similarity between 2 orbits. For comparison, the asteroids 2005 UD and 1999 YC from the IAU database are also proposed for similarity tests because former ground-based observations estimated that about 1012 ∼1013 kg of mass had been dispensed to the Geminid meteor shower (Jenniskens 1994)[22], which is in 185

excess of the mass of 3 × 105 kg ejected from each encounter of Phaethon at the perihelion (Jewitt et al. 2013)[23]. Jewitt and Hsieh (2006)[24] suggested that the mass loss of Geminid stream may arise from the Phaethon-Geminid complex (asteroid Phaethon, (155140) 2005 UD and asteroid (225416) 1999 YC5) which originated from one breakup event and was associated with one of the big

190

asteroid, 2 Pallas (de Leon et al 2010)[25]. The calculated Dsh of these three asteroids are given in Table 6. Notice that although there were identified 53 meteor orbits belonging to Geminids, only 39 orbits were selected using iterative method with Dsh ≤0.15. The detailed orbital elements of these 39 orbits can be found in Appendix A.7. However, if we take a look carefully in Appendix A.7,

195

we find that some orbits with relatively low and high inclination angle, corresponding to the Dsh about 0.090 ∼0.146, to asteroid (3200) Phaethon’s orbit still remain. In other words, the orbits with high-threshold (a low Dsh ) have to be taken into account in the future analysis. From table 6 and Appendix A.7, where the average value and the individual value of Dsh is actually smaller than

200

the 0.15 matching criterion, it is concluded that the observed orbits of Geminid meteor shower and the Phaethon’s orbit are in positive interrelation.

14

5. Discussion and Summary Recent operations of the TDMS have advanced a growing database, which 205

provides profuse data sets readily available for examining the linkages connecting the meteor orbital characteristics with their associated parent asteroids. By taking the Geminids as a proto-typical practice, it is shown that the comparison of the orbital elements of the Geminid meteoroids with its parent 3200 Phaethon shows good agreement. Although the results of the orbital elements

210

with the other 2 asteroids, 2005 UD and asteroid 1999 YC show inconsistency, we still cannot rule them out as the candidates of the shower’s progenitor. While stringent constrains on the orbit evolution are essential for gaining accurate knowledge about the mechanism behind the breakup, captures of sufficient meteors with precise orbit elements are fundamental for desired orbital anal-

215

yses. It is noticed that since its start into operation, from an around 2-year session of observations, TDMS acquired just about 7% of meteors detected with orbital elements. To deal with this circumstance, we have set up a new site in mid-2018, Fushoushan Farm, where the observation conditions, including historical weather records and geographical aspects, are comparable with Lulin

220

observatory. Indeed, the efficiency of the network was increasing dramatically in late-2018 from 1% to 7%. We hope, in the future, to accomplish observations with more meteor detections and orbit determinations for improving our knowledge of the orbital characteristics of meteor showers. In summary, we arrive at the following concluding remarks:

225

1. The TMDS gathered 676 precise orbits of meteors captured during operations from 2016 to 2018. Analyzes of the orbit data sets provide an effective approach to attain information of relevance to activities of the meteor parent bodies (i.e. Near-Earth Asteroids or Comets). 2. The present conduction of the TDMS to observations in the 2017 an 2018

230

Geminid meteor shower yielded 39 precisely determined meteor orbits. From analyzes of the Dsh parameters in these orbits, the associated parent body is uniquely identified: namely, the 3200 Phaethon. A result agrees with the finding

15

unfolded from former investigations of Geminid in the literature. It is worthwhile to note that the TDMS proved to be highly efficacious in deciding the 235

parent bodies of meteor showers, though it is not satisfactorily efficient for capturing meteors with deterministic orbits. Once the efficiency in determining meteor orbits can be substantially increased, it is anticipatable that the TDMS will be capable of providing prolific meteor-shower events for advanced studies. For improving the efficiency of the TDMS to detect meteor events in conjunc-

240

tion with orbits, the site locations selected for installations play a crucial role. Deployment of additional observation stations at suitable locations to achieve sufficient concurrent meteor detections with orbital information is one of the primary tasks called for the future development of the TDMS.

Acknowledgements 245

We specially acknowledge that the Lulin staff, Chi-Sheng Lin and HsiangYao Hsiao have provided assistance in observations. This publication has made use of data collected at Lulin Observatory, partly supported by MOST grant 105-2112-M-008-024-MY3. This work was also supported by MOST 105-2112M-008-002-MY3 from the Ministry of Science and Technology of Taiwan.

250

Appendix A. Orbital elements

16

Table A.7: The Geminid orbital elements including the six basic parameters and orbital period are all derived by the UFOOrbit software. The standard deviation for these 39 orbits in semi-major axis, perihelion distance, eccentricity, orbital period, argument of perihelion, longitude of the ascending node, and inclination are 0.32, 0.02, 0.02, 0.67, 2.3, 0.6, 3.5 respectively.

Orbit no.

MJD

semi-

perihelion eccentricity orbital

argument

longitude

major

distance

of

of the as-

period

17

axis

peri-

helion

inclination Dsh

cending node

(stations)

(au)

(au)

(year)

(deg)

(deg)

(deg)

Phaethon

1 (Lulin, KTO)

58101.66

1.53

0.13

0.92

1.90

324.8

262.6

21.6

0.03

2 (Lulin, KTO)

58101.67

1.71

0.14

0.92

2.23

323.0

262.6

27.8

0.11

3 (Lulin, KTO)

58101.67

1.93

0.13

0.93

2.68

322.9

262.6

25.6

0.08

4 (Lulin, KTO)

58101.67

1.50

0.13

0.91

1.83

324.7

262.6

23.8

0.04

5 (Lulin, KTO)

58101.71

1.62

0.15

0.91

2.05

321.4

262.7

17.5

0.09

6 (Lulin, KTO)

58101.72

1.91

0.13

0.93

2.64

323.4

262.7

22.9

0.05

7 (Lulin, KTO)

58101.73

1.77

0.12

0.93

2.36

324.9

262.7

28.9

0.13

18

8 (Lulin, KTO)

58101.76

1.76

0.12

0.94

2.34

325.9

262.7

28.8

0.13

9 (Lulin, KTO)

58101.76

1.90

0.11

0.94

2.62

326.6

262.7

28.6

0.13

10 (Lulin, KTO)

58101.77

2.07

0.13

0.94

2.98

323.1

262.7

24.7

0.07

11 (Lulin, KTO)

58101.77

1.54

0.12

0.92

1.91

326.1

262.7

27.6

0.10

12 (Lulin, KTO)

58101.82

1.72

0.14

0.92

2.26

321.8

262.8

24.0

0.05

13 (Lulin, KTO)

58101.83

1.87

0.12

0.93

2.56

324.2

262.8

27.2

0.10

14 (Lulin, KTO)

58101.83

1.61

0.14

0.91

2.04

322.5

262.8

27.5

0.10

15 (Lulin, FSS)

58464.75

1.41

0.17

0.88

1.67

320.5

260.4

18.9

0.10

16 (Lulin, KTO)

58464.75

1.15

0.14

0.88

1.23

327.0

260.4

14.6

0.14

17 (Lulin, KTO)

58465.52

1.32

0.14

0.90

1.52

325.0

261.2

24.1

0.04

18 (Lulin, KTO)

58465.67

1.84

0.13

0.93

2.50

323.8

261.3

23.9

0.06

19 (Lulin, KTO)

58466.53

1.34

0.14

0.90

1.54

324.8

262.2

24.2

0.04

20 (Lulin, KTO)

58466.56

1.44

0.13

0.91

1.73

324.8

262.2

22.9

0.03

21 (Lulin, KTO)

58466.60

1.55

0.13

0.92

1.92

324.9

262.3

27.6

0.10

22 (Lulin, KTO)

58466.59

1.52

0.13

0.91

1.87

324.6

262.3

24.0

0.04

23 (Lulin, KTO)

58466.62

1.98

0.11

0.94

2.79

325.3

262.3

29.5

0.14

24 (Lulin, KTO)

58466.65

1.89

0.11

0.94

2.59

325.8

262.3

26.7

0.10

25 (Lulin, KTO)

58466.66

1.89

0.11

0.94

2.59

325.8

262.3

26.7

0.09

26 (Lulin, KTO)

58466.67

1.96

0.11

0.94

2.75

325.8

262.4

28.1

0.12

19

27 (Lulin, KTO)

58466.67

1.27

0.10

0.92

1.44

330.5

262.4

25.7

0.10

28 (Lulin, KTO)

58466.68

1.27

0.11

0.95

2.81

325.9

262.4

29.7

0.15

29 (Lulin, KTO)

58466.69

1.41

0.10

0.93

1.68

329.9

262.4

21.3

0.08

30 (Lulin, KTO)

58466.74

1.76

0.12

0.93

2.33

325.2

262.4

28.6

0.12

31 (Lulin, KTO)

58466.74

1.66

0.11

0.94

2.14

327.5

262.4

26.7

0.10

32 (Lulin, KTO)

58466.75

1.91

0.14

0.93

2.64

321.3

262.4

25.6

0.08

33 (Lulin, KTO)

58466.78

1.52

0.12

0.92

1.87

326.3

262.5

26.3

0.08

34 (Lulin, KTO)

58466.80

1.63

0.12

0.93

2.08

326.3

262.5

26.7

0.09

35 (Lulin, KTO)

58466.81

2.67

0.11

0.96

4.35

324.5

262.5

26.0

0.10

36 (Lulin, KTO)

58466.84

1.13

0.14

0.88

1.21

327.1

262.5

19.2

0.06

37 (Lulin, FSS)

58466.84

1.39

0.16

0.89

1.65

321.8

262.5

20.6

0.05

38 (Lulin, FSS)

58466.88

2.59

0.14

0.95

4.17

320.2

262.6

27.9

0.13

39 (Lulin, FSS)

58466.78

1.43

0.14

0.91

1.70

324.6

264.5

21.6

0.03

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Highlights We have increased the font size of Figs 3 and 4.

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Author’s name Affiliation Zhong-Yi Lin Institute of Astronomy, NCU Hsin-Chang Chi Department of Physics, NDHU Bo-Hao Wang Department of Applied Mathematics, NDHU Zong-Yi Lin Department of Physics, NDHU Chih-Cheng Liu Department of Applied Mathematics, NDHU Jim Lee Taipei Astronomical Museum, Taipei, Hung-Chin Lin Institute of Astronomy, NCU Bingsyun Wu Taichung municipal Hui-Wen high school, Taichung Xue-Hui Ma/Chia-Hsien Liao Ken-Ting Observatory, NTU