CN105892031A - Method for simultaneously observing bright source and dark source in multi-object fiber spectroscopic observation - Google Patents

Abstract

The invention discloses a method for simultaneously observing a bright source and a dark source in multi-object fiber spectroscopic optical telescope observation with the dark source being not polluted by the light source. The method comprises the steps of inputting a bright star catalog and an observation target star catalog, acquiring the atmospheric seeing by using weather monitoring software, determining an observation star magnitude range, wherein when a bright source beyond the specified star magnitude range is required to be observed, coordinates of the target need to be biased, acquiring the dynamic efficiency of a point source model according to the seeing under the condition of unbiased positioning of an optical fiber, determining the star magnitude required by turning the light source into dark, calculating the arc seconds that the optical fiber needs to be biased , wherein if the light source required to be observed has no source within 60 arc seconds, right ascension or declination coordinates of the source can be biased directly; and if a target exists in 60 arc seconds of the light source required to be biased, the light source deviates in the direction away from the source which has a great influence on the light source, the influence imposed on the biased source by an adjacent light source cannot be ignored after being biased, the source is not arranged to be observed, otherwise, the source is arranged to be observed.

Description

The method that in multi-object fiber spectrographs observation, bright source and dark source are observed simultaneously

Technical field

The present invention relates to a kind of multi-object fiber spectrographs astronomical telescope and observe bright source and the skill in dark source simultaneously Art, is particularly suited for the optical spectra observation system that number of fibers is a lot.

Background technology

The optical spectra studying remote celestial body can obtain abundant physical message.Astronomy to be solved and celestial body The many advanced problems of physics, need to obtain the optical spectra of a large amount of celestial body.The most a lot of countries are all Have the multi-object fiber spectrographs astronomical telescope of oneself.The large sky area multiple target optical fiber of China Spectrum astronomical telescope (LAMOST) has heavy caliber and big visual field concurrently, is that spectrum is seen the most in the world Survey the telescope that acquisition rate is the highest.LAMOST is the large sky area multiple target of China's independent research Fiber spectroscopic telescope, it is by reflecting schmidt plate, primary mirror sphere with middle Jiao Face is constituted.The light of celestial body is reflected Schmidt corrector and reflexes to primary mirror sphere, then through primary mirror sphere It is imaged on focal plane after reflection.LAMOST telescope has 5 degree of visual fields, focal plane a diameter of 1.75 Rice, focal plane is placed 4000 optical fiber.The optical fiber placed on focal plane, passes respectively by the light of celestial body It is passed on the slit of spectrogrph, then obtains thousand of by the ccd detector after spectrogrph simultaneously The spectrum of celestial body.

Under normal circumstances, observing at multi-object fiber spectrographs as LAMOST, two adjacent More than 5 magnitudes of magnitude difference of observation celestial body, then the contour line wing meeting in bright source on ccd detector Pollute adjacent dark source optical fiber.Magnitude (magnitude) is the amount weighing celestial body luminosity, magnitude Being worth the least, star is the brightest；The numerical value of magnitude is the biggest, and star is the darkest.Generally at multiple target optical fiber light In spectrum observation, in order to avoid the pollution in bright source, it is desirable to the target magnitude model in same observation sky district It is trapped among in 5 magnitudes.But wish the most again can observe magnitude difference in same sky district away from relatively simultaneously Big bright source and dark source.If meeting the bright source of minority on the basis of not affecting dark source observation effect Observation, then can improve observed efficiency.

Bright source and the method in dark source can be observed in same sky district it is therefore desirable to have a kind of simultaneously, come Meet observation requirements, improve observed efficiency.

Summary of the invention

For the problems referred to above, it is proposed that a kind of coordinate to bright source is biased reducing it enters light The method of fine photon, this method can make bright source and dark source be seen in same sky district simultaneously Survey.This method neither affects the observation effect in dark source, can meet again the observation need in some bright sources Ask.This technology is not only used in LAMOST observation, it is also possible to be used in other many mesh On the telescope of mark fiber spectrum.

The present invention proposes a kind of can observe bright source and dark source in multi-object fiber spectrographs is observed simultaneously Method, to meet observation requirements, improves observed efficiency, and the method makes in a Ge Tian district domestic demand When bright source target to be observed is less, bright source and dark source can be observed simultaneously, be avoided that again bright source pair The pollution of dark source optical fiber.

In one aspect, the present invention relates to one avoids bright source to take turns in multi-object fiber spectrographs is observed The profile wing pollutes adjacent dark source optical fiber, makes the bright source in same sky district and dark source to observe simultaneously The method arrived, specifically, the method is, bright source is carried out coordinate biasing, bright for original alignment The optical fiber in source in situ on the basis of remove a certain distance, reduce and enter in optical fiber Number of photons, checks after biasing and is biased whether bright source is polluted by other bright stars.

In yet another aspect, the method that the present invention relates to a kind of bright source coordinate biased direction, specifically Ground, the method makes to be biased the directly biasing that do not has target source near bright source in 60 rads, and this is bright The declination in source or right ascension coordinate；Many bright sources are had, then towards to it by 60 rads of bright source of biasing The opposite direction biasing in that source that impact is maximum.

In yet another aspect, the present invention relates to a kind of bright source coordinate biasing means, concretely comprise the following steps:

A) in the case of fiber orientation zero deflection, point source dynamic efficiency is relevant with seeing, depending on peaceful Degree can be obtained by the weather monitoring data of every day, then by seeing, can be calculated point source Dynamic efficiency；

If b) magnitude range that the magnitude in a bright source specifies beyond a Ge Tian district, then need Bias its coordinate, and then the number of photons making it into optical fiber reduces, the rad number of skew and bright The magnitude in source needs dimmed magnitude relevant with it；

If c) a bright source needing observation, does not has adjacent target in 60 rads, then biases The declination in this source or right ascension, if active in 60 rads near bright source, then to its flow The rightabout skew in the source that impact is maximum, if after Pian Zhi, the neighbouring bright source shadow to this source Sound can not be ignored, then abandon the observation to this source, without impact, then retains observation.

In actual observation, both need to consider that other to be observed the shadow in dark source by the bright source needing observation Ring, also to consider other bright source impacts on source to be observed of objective reality in observation sky district. Needing to input observational catalogue when observation, this star catalogue is generally only the observation that scientists is concerned about Target source, but it is not all of target.When biasing bright source coordinate, in addition it is also necessary to know except observation Outside the bright source of star catalogue, the information in the bright source of other objective realities in this day district.Avoid bright The pollution in source will include all of bright source in day district.Bright source star catalogue can download hipparcos catalogue (HIP, limiting magnitude is 13 etc.) and USNO-US Naval Observatory star catalogue (UCAC, limit star Etc. for 21 etc.), the two star catalogue takes its intersection less than being complete in the range of 16 grades. When calculating bright star and affecting, the bright star in these star catalogues should be comprised.

Accompanying drawing explanation

Fig. 1 is the observed object magnitude-Between Signal To Noise Ratio figure in a Ge Tian district, and coordinates of targets is Original coordinates；

Fig. 2 is the observed object magnitude-Between Signal To Noise Ratio figure in a Ge Tian district, bright in the mesh of 15 grades Target coordinate is biased, and its number of photons on optical fiber that falls is equivalent to the target of 15 grades,

Fig. 3 is signal to noise ratio change before and after the coordinate biasing of same source.

Fig. 4 is the flow chart that in multi-object fiber spectrographs observation, bright source and dark source are observed simultaneously

Detailed description of the invention

For making the object, technical solutions and advantages of the present invention clearer, by following embodiment party Formula combines accompanying drawing, and the present invention is described in detail.

The present invention reaches to reduce its purpose entering optical fiber number of photons, phase by biasing bright source coordinate When in reducing the magnitude in bright source, make bright source and dark source can observe in a Ge Tian district simultaneously.Enter Row-coordinate biasing first has to calculate definite offset angle number of seconds and biasing side according to specific needs To.The magnitude that offset angle number of seconds and the original magnitude in bright source and needs reduce is directly related.Below Describe in detail as making certain bright source be reduced to certain magnitude, the meter of the rad number that its coordinate is to be biased Calculation method.

Step 1, in the case of fiber orientation zero deflection, point source dynamic efficiency is relevant with seeing, Seeing can be obtained by the weather monitoring data of every day.Generally represent air with atmospheric seeing Extension effect to point source, it is equivalent to the full width at half maximum of point spread function.

$\mathrm{seeing}=2\sqrt{2\ln 2}{r}_0---\left(1\right)$

Wherein seeing is seeing, r₀The full width at half maximum of point spread function, seeing substitute into by Formula (1) can obtain the full width at half maximum of point spread function.

The dynamic efficiency of point-source model is:

$\mathrm{\η}=\underset{{(x-c)}^2+y^2={r_c}^2}{\∫\∫}\frac{1}{2\mathrm{\π}{r_c}^2}{e}^{-\frac{(x^2+y^2)}{2{r^2}_0}}\mathrm{dxdy}---\left(2\right)$

Wherein (x-c)²+y²=r_c ²Represent fiber end face and focal plane star image coupling unit, r_cRepresent fiber cross-sections Radius, from concrete telescope optical fiber, r₀It it is the point spread function drawn by formula (1) Full width at half maximum, c is the rad number at observed object stray fiber center.

Step 2, if a magnitude is m^*Source beyond the magnitude range that specifies of observation sky district, Then need to bias its coordinate, and then reach to reduce its purpose entering optical fiber number of photons.Can be by needing Magnitude coordinates computed amount of bias to be biased to.Magnitude is m^*If source make it be collected by optical fiber Number of photons is equivalent to the source of m magnitude, and its center needs the rad number offset permissible relative to fiber optic hub Derived by formula below:

$\underset{{(x-c)}^2+y^2={r_c}^2}{\∫\∫}\frac{1}{2\mathrm{\π}{r_0}^2}{e}^{-\frac{(x^2+y^2)}{2{r^2}_0}}\mathrm{dxdy}=\mathrm{\η}{\×10}^{\frac{m^{*}-m}{2.5}}---\left(3\right)$

The c calculated by formula (3) is exactly the rad number that optical fiber needs skew.

C=3600 × arccos (sin δ₀sinδ₁+cosδ₀cosδ₁cos(α₁-α₀)) (4)

Step 3, in formula (4), c is the optical fiber rad number needing skew, α₀、δ₀Before being source biasing Right ascension, declination coordinate, α₁、δ₁It is the right ascension after biasing, declination coordinate.Can from formula (4) To show that coordinate moves a rad and moves a rad corresponding to latitude, or right ascension moves 1/cos(δ₀) individual rad.If a bright source, in 60 rads, there is no adjacent target, the most permissible Directly bias declination or the right ascension in this source.If it is active in 60 rads, then away to it The direction skew in the source that flow effect is maximum, so can reduce the pollution to adjacent source.If offseting it After, the impact of bias source be can not ignore by neighbouring bright source, then, when arranging surveillance program, it is right not arrange The observation of this bias source, on the contrary then bias successfully, arrange observation.

As a example by certain observation of LMAOST telescope, the detailed process of bright source coordinate biasing is described.? The illustrative example of this present invention is used for explaining the present invention, but not as a limitation of the invention.

Observed object to district on the same day, is carried out respectively by original coordinates with to the coordinate after the biasing of bright source Observation, this example, the method biased by coordinate less than the observed object of 15 grades, allows it pass through light Fine flow is equivalent to the target of 15 grades.

Below, bright star biasing process is described in detail, including following steps:

Step 101 inputs observed object star catalogue and bright source star catalogue.Observational catalogue comes from scientist to be provided, At this example star catalogue downloaded from SDSS, bright source star catalogue downloads UCAC and HIP star from website Table.

Step 102 determines observation magnitude range, it is thus achieved that weather seeing numerical value, bright source in calculating observation Need the rad number of biasing.Magnitude range is defined to 15-18 etc. in this example, less than 15 grades Source needs to bias coordinate so that it is the number of photons entering optical fiber is equivalent to the source of 15 grades.Utilize formula (3) The rad number needing biasing less than the source of 15 grades can be calculated.Observation instrument is in County, Hebei Province, China The LAMOST telescope of Xinglong County, observation time is evening on January 2nd, 2012, and that night regards peaceful Degree is 4.8 rads.Observation sky district is 0102_TM1_nooff and 0102_TM1_off, 0102_TM1_nooff be bright source coordinate through biasing sky district, 0102_TM1_off be bright in Observation sky district after the coordinate biasing in the sources such as 15.The original observed object in the two sky district is the same, Bright source coordinate biasing in different is exactly a Ge Tian district, a not biasing.

Step 103 determines biased direction.If it is the brightest in 60 rads around the bright source A biased Target, then can directly bias declination or right ascension；If by around the bright source A of biasing 60 rads Inside have one bright in the source of 15 grades, then to away from this Liang Yuan direction bias；If being biased bright source A Around there are many bright sources, then away from that the source direction biasing maximum on its impact.Such as from quilt Bias the source having one 14 grade at bright source A 12 rads, and have one 6 grade at 15 rads from A Source, from formula (3), on A impact big be the source of 6 grades at 15 rads rather than from it The source of 14 grades at 12 rads.At this moment it is accomplished by its coordinate away from that source at 15 rads Direction biases.

Check after the biasing of step 104 coordinate, see and whether affected by adjacent objects.Bright source coordinate After biasing, more whether affected by other bright sources neighbouring with the coordinate calculating after biasing, it is judged that standard Whether the magnitude difference for magnitude after biasing and neighbouring bright source is more than 5 magnitudes.Without more than 5 Magnitude does not the most affect reservation observation, if had an impact, that gives up in observation that this is biased is bright Source.Accompanying drawing 1 is the magnitude-Between Signal To Noise Ratio figure of the front observed object of biasing, and accompanying drawing 2 is that bright source coordinate is inclined After putting.From accompanying drawing 2 can find out the star less than 15 grades after biasing, the signal to noise ratio observed and The astrology of 15 grades is worked as.Having some discrete points in attached Fig. 1 and 2 is due to indivedual bad optical fiber and instrument Performance causes.0102_TM1_nooff with 0102_TM1_off is different due to observation time, instrument The reasons such as device unstable properties, their signal to noise ratio-magnitude corresponding relation is different.District is not on the same day Problem more can be reflected with the signal to noise ratio difference of magnitude.What accompanying drawing 3 was listed is the source of 13.92 magnitudes The representative instance of observed result.This source is biased to 15.0 etc. by 13.92 etc. needs to bias 3.34 rads, Target is not had, so having biased the right ascension coordinate in this source owing to this source is neighbouring.Observation before biasing In this source signal to noise ratio be 39.8, be 1.87 times of (noises such as 15 of district 15 target signal to noise ratio such as grade on the same day Than average out to 21.3)；After this source biasing coordinate, signal to noise ratio is 27.0, is the target such as district 15 on the same day 1.04 times (15 etc. signal to noise ratio average out to 25.9) of signal to noise ratio.Thus result finds out the source of 13.92 grades After biasing, flow and 15 etc. source be suitable.

Claims (3)

1. avoid the bright source contour line wing to pollute an adjacent dark source optical fiber in multi-object fiber spectrographs is observed, Make the method that the bright source in same sky district and dark source can observe simultaneously, including input observational catalogue and Bright source star catalogue, it is stipulated that observation magnitude range, is characterized in that: see for needing outside magnitude range The bright source surveyed carries out coordinate biasing, the original optical fiber being directed at bright source in situ on the basis of move Open a certain distance, reduce and enter into the number of photons in optical fiber, check after biasing and biased bright source Whether polluted by other bright stars.

Bright source the most according to claim 1 coordinate biasing means, is characterized in that: biased near bright source Directly biasing declination or the right ascension coordinate of target source is not had in 60 rads；By 60 jiaos of bright source of biasing There are many bright sources second, then towards the opposite direction biasing in that source maximum on its impact.

Bright source the most according to claim 1 and 2 coordinate biasing means, is characterized in that:

A) in the case of fiber orientation zero deflection, point source dynamic efficiency is relevant with atmospheric seeing, depending on peaceful Degree can be obtained by the weather monitoring data of every day, then by seeing, can obtain the dynamic of point source State efficiency；

If the b) magnitude range that the magnitude in a bright source specifies beyond a Ge Tian district, then need biasing Its coordinate, and then the number of photons making it into optical fiber reduces, the rad number of skew and bright source Magnitude needs dimmed magnitude relevant with it；

If c) a bright source needing observation, does not has adjacent target source, then to offset this in 60 rads The declination in source or right ascension, if having many sources, then to it at this in 60 rads near bright source The rightabout biasing in the source that flow effect is maximum, if after Pian Zhi, neighbouring bright source is to this source Impact can not ignore (i.e. after biasing magnitude and adjacent bright source magnitude difference more than 5 magnitudes), Then abandon the observation to this source, otherwise retain.