CN108469418B

CN108469418B - Method for measuring FGK type star metal abundance and optical filter VSAGE

Info

Publication number: CN108469418B
Application number: CN201810162482.9A
Authority: CN
Inventors: 范舟
Original assignee: National Astronomical Observatories of CAS
Current assignee: National Astronomical Observatories of CAS
Priority date: 2018-02-27
Filing date: 2018-02-27
Publication date: 2020-01-10
Anticipated expiration: 2038-02-27
Also published as: CN108469418A

Abstract

The invention relates to the field of astronomical measurement, and provides a method for measuring the abundance of FGK type star metal and an optical filter v_SAGEThe center wave of the filterThe length of the filter is 395nm, the bandwidth of the filter is 29nm, and the filter can cover CaII H&And K absorption lines are used for accurately measuring the absorption spectral lines, so that the abundance of the star metal is effectively measured. The measuring method comprises the following steps: observing and processing data of the FGK type fixed star and the flow standard star to be detected; fitting an atmospheric extinction curve and calibrating the flow of the fixed star to be measured; pair of "(v)_SAGE-g) - (g-i) color-to-metal abundance relationship [ Fe/H]"fitting; and (4) solving the metal abundance of the fixed star to be detected by a photometric method. The method has high observation efficiency on the FGK type stars, is simple in metal abundance measurement method, can measure the metal abundance of all the FGK type stars in an observation field at one time, has high speed compared with the traditional method, has no selective effect, and is suitable for measuring and counting the metal abundance of the stars in a large sample.

Description

Method for measuring FGK type star metal abundance and optical filter VSAGE

Technical Field

The invention relates to the technical field of astronomical measurement, in particular to a method for measuring the abundance of FGK type star metal and an optical filter v_SAGE。

Background

There are many methods for measuring the abundance of FGK-type sidereal metals, and conventionally, the intensities of Fe lines are measured by using spectral observation, and calculation is performed assuming local thermodynamic equilibrium LTE, and the measurement can also be performed based on some other spectral line measurement sensitive to the abundance of metals, such as CaII H & K line (393.4/396.8nm), CaII triplet line (849.8/854.2/866.2nm), and the like. However, for spectral observation, much observation time is required, and conventional photometric systems such as Johnson-CousinbVRI and SDSS ugriz are not sensitive to spectral lines because the bandwidths are too wide.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for measuring the abundance of FGK type star metal and an optical filter v_SAGEThe filter is specially designed v_SAGEAnd the wave band filter can accurately reflect the metal abundance of the FGK type stars.

The invention is realized by the following technical scheme:

filter v for effectively measuring FGK type star metal abundance_SAGEThe filter v_SAGEThe central wavelength is 395nm, the bandwidth of the optical filter is 29nm, and CaII H can be well covered&And measuring the absorption line, wherein the equivalent width of the absorption line has good correlation with the metal abundance of the stars, and the metal abundance of the stars is effectively measured by measuring the intensity of the line, so that the metal abundance of the FGK type stars is determined.

A method of measuring the abundance of FGK-type sidereal metals, comprising the steps of:

firstly, observing and processing data of FGK type fixed stars to be detected;

observing and processing the flow standard star;

fitting an atmospheric extinction curve and calibrating the flow of the fixed star to be measured;

step four, pair ″ (v)_SAGE-g) - (g-i) color-to-metal abundance relationship [ Fe/H]"fitting;

and step five, calculating the metal abundance of the fixed star to be detected by a photometric method.

Further, the first step specifically includes:

step 1.1) acquiring a background image, a multiband flat field image and a dark field image of a telescope; the multiple bands are v_SAGEA/g/i waveband;

step 1.2) observing the FGK type fixed star to be measured by utilizing a telescope, wherein v is used during observation_SAGEThe wave band optical filter and the g/i wave band optical filter are respectively observed; controlling exposure time, and checking the point spread function PSF outline of the star image in real time to ensure that the star image is not elongated and has no virtual focus;

step 1.3) combining background images, carrying out background correction on observation images of all to-be-detected FGK type stars, and eliminating bias voltage and non-uniformity influences of a detector and photoelectric observation equipment; for the observed star image to be detected, the combined background image at the current night is subtracted;

step 1.4) dark field correction is carried out, and the influence of dark current on the detector is eliminated;

step 1.5) flat field correction is carried out, and the influence of the illumination of an optical system and the pixel response difference of a CCD detector is eliminated;

step 1.6) v-treatment of fixed stars to be tested_SAGEAnd measuring light of the observation image in the wave band and the g/i wave band.

Further, the second step specifically comprises:

step 2.1) v-flow Standard Star_SAGEObserving the wave band and the g/i wave band, wherein the observation needs to be performed at a photometric night, and the atmosphere is stable and cloudless at night; controlling exposure time, checking point spread function PSF contour of star image in real time and ensuring that the point spread function PSF contour does not existElongation and no appearance of virtual focus;

step 2.2) convection current standard star v_SAGECorrecting background, dark field and flat field of observation images of wave bands and g/i wave bands;

step 2.3) v-flow Standard Star_SAGEAnd performing photometry on the images of the wave bands and the g/i wave bands to obtain the instrument star and the like.

Further, the third step specifically comprises:

step 3.1) calculating the atmospheric mass of the flow standard star, and fitting an atmospheric extinction curve;

calculation formula of atmospheric mass:

v_cali-v_inst＝k_0,v+k_1,vχ+k_2,v(v_cali-g_cali) (4)

g_cali-g_inst＝k_0,g+k_1,gχ+k_2,g(g_cali-i_cali) (5)

i_cali-i_inst＝k_0,i+k_1,iχ+k_2,i(g_cali-i_cali) (6)

in the above formula, k_0,v,k_0,gAnd k_0,iIs the zero point of the instrument, k_1,v,k_1,gAnd k_1,iIs the main extinction coefficient, k_2,v,k_2,gAnd k_2,iIs that the secondary extinction coefficient is related to color, and χ is the mass of the atmosphere, and can be calculated by the following method:

χ＝sec z (7)

wherein z is the zenith angle, the formula is applicable to the range of the zenith angle z < 60-75 ℃;

carrying out flow calibration on the observation data of the sidereal at the night through the multi-band observation standard star at the photometric night and fitting the extinction curve;

step 3.2) utilizing the atmospheric extinction curve to carry out flow calibration on the fixed star to be detected:

v of FGK type star to be measured_SAGEBringing instrument stars and the like of the/g/i wave band into the atmospheric extinction curve obtained in the step 3.1) by fitting to obtain calibration stars and the like outside the atmosphere; for each bandThe star, etc. should bring the atmospheric extinction curve into the corresponding band.

Further, the fourth step specifically includes:

step 4.1) selecting proper FGK type constellations from Kurucz star atmosphere model and convolving the samples to obtain v_SAGEA/g/i band star, etc.;

step 4.2) fitting Kurucz fixed star atmosphere model (v)_SAGE-g) - (g-i) colour-metal abundance [ Fe/H]The relationship (2) of (c).

Further, the fifth step specifically comprises:

step 5.1) scaling the observations_SAGE(v) obtained by star-to-star fit of/g/i waveband FGK type star_SAGE-g) - (g-i) colour-metal abundance [ Fe/H]Correlating to obtain the abundance of the metal;

and 5.2) sorting the metal abundance results of the obtained FGK type stars to be detected, and generating a table with a fixed format according to the requirements.

Further, in the first step, when observing the FGK type sidereal to be measured, an optical filter v for effectively measuring the metal abundance of the FGK type sidereal is adopted_SAGEThe filter v_SAGEThe center wavelength is 395nm, and the filter bandwidth is 29 nm.

Further, in step 4.1), the Kurucz sidereal atmosphere model is convolved to obtain the v of the sidereal by the following formula_SAGEThe/g/i wave band star is equal:

the convolution formula for the Vega system is as follows:

MAG_Vega(Obj)＝-2.5log(∫{F_l(Obj)S_λdλ}/∫{F_l(Vega)S_λdλ}) (8)

MAG_Vega(Obj)＝-2.5log(∫{F_ν(Obj)S_νdν}/∫{F_ν(Vega)S_νdν}) (9)

the convolution formula for the AB system is as follows:

MAG_AB(Obj)＝-2.5log(∫{F_ν(Obj)S_νdν}/∫{S_νdν})-48.6 (10)

where λ is the wavelength, v is the frequency, F_ν(Obj) is the flow of the celestial body in ergs^-1cm^-2Hz^-1，S_νIs the corresponding curve of the instrument, F_ν(Vega) is the flow rate of Neisseria hernalis in ergs^-1cm^-2Hz^-1。

The invention has the beneficial effects that:

1. v designed by the invention_SAGEThe optical filter is easy to manufacture, low in cost and simple in installation and observation operation, the observation and metal abundance measurement method for the FGK type fixed star by utilizing the optical filter is simple, convenient to apply and popularize and strong in applicability, and the optical filter can be applied to various different observation systems;

2. compared with the traditional method for measuring metal abundance by spectrum, the exposure time is greatly shortened, and all fixed stars in the field of view can be measured, so the observation efficiency is greatly improved, and no selection effect exists, therefore, the novel optical filter v_SAGEAnd the FGK type sidereal metal abundance method provides good technical support for the rapid, efficient and accurate measurement of the metal abundance of sidereal;

3. the method has high observation efficiency on the FGK type stars, is simple in metal abundance measurement method and high in efficiency, can measure the metal abundance of all the FGK type stars in an observation field at one time, has greatly accelerated speed compared with the traditional spectral measurement method, has no selection effect, and is very suitable for measuring and counting the metal abundance of stars of large samples.

Drawings

Fig. 1 is a flow chart illustrating a method for measuring the abundance of FGK-type sidereal metals according to an embodiment of the present invention.

FIG. 2 shows v in an embodiment of the present invention_SAGEFilter response curves.

Fig. 3 is a schematic diagram of aperture photometry.

FIG. 4 shows a correction of the growth curve.

FIG. 5 is a graph showing the extinction curve (v) of the atmosphere_SAGEA band).

FIG. 6 shows the log of 4.5, effective temperature T, obtained from the Kurucz sidereal atmospheric model_eff(v) of FGK-type stellar in case of 4500-_SAGE-g) - (g-i) colour-metal abundance [ Fe/H]"schematic diagram of relationship.

Detailed Description

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that technical features or combinations of technical features described in the following embodiments should not be considered as being isolated, and they may be combined with each other to achieve better technical effects. In the drawings of the embodiments described below, the same reference numerals appearing in the respective drawings denote the same features or components, and may be applied to different embodiments.

In the present invention, FGK-type stars are taken as an example of the observation target, but this is not restrictive, and includes any observation target of a star group (e.g. celestial bodies such as a starry group, a galaxy, etc.) composed of or mainly composed of FGK-type stars.

The embodiment of the invention provides a v for measuring the abundance of FGK type sidereal metals_SAGEOptical filter, the optical filter v_SAGEThe central wavelength is 395nm, the bandwidth of the optical filter is 29nm, and CaII H can be well covered&K absorption line, measuring the absorption line, thereby determining the metal abundance of the FGK-type stars.

Another embodiment of the present invention provides a method for measuring the abundance of FGK-type sidereal metals, which is illustrated in the flow chart of fig. 1, and the detailed steps are as follows:

the method comprises the following steps: observing and processing data of FGK type fixed star to be measured

Preferably, the steps specifically include:

step 1.1) acquiring background image (Bias) and multiband (v) of telescope_SAGEA/g/i band), a Dark field image (Dark), etc.;

for photometric observation, the final processing precision is affected by the uniformity, linearity and responsivity of the optical system (including the light source) and the detector, so that the preprocessing of photometric requires that the pixel difference between the pixels of the CCD and the difference of the optical system are eliminated, and the image distortion and the like are corrected; to ensure the data processing accuracy, a batch of images for system correction is required, which mainly comprises: background image (Bias), Flat field image (Flat) and Dark flow image (Dark).

Background (Bias) images, such as the typical nightly data, contain 10-20, ADU readings typically between 500 and 2000 depending on the different CCD or CMOS camera settings.

For Dark field (Dark) images, mainly the Dark current of the detector itself is eliminated; keeping consistent with the exposure time during shooting; typical one hour dark current for current scientific grade CCD cameras is around 1-2e^-1Around/pixel, therefore for short exposures: (<10 minutes) if the requirement of the photometric accuracy is not high, the influence can be ignored.

Flat field (Flat) images require the use of v separately_SAGEThe filters with wave bands and g/i wave bands shoot sky light or a dome built-in screen; for a flat field of sky, a clear sky before sunrise or after sunrise without clouds may be photographed, and a sky far from the sun is generally selected to reduce a brightness gradient in the field of view (the sky before sunrise is directed to the west, and the sky after sunrise is directed to the east). The reading of flat-field ADU is well between 15000 and 25000, and in order to ensure sufficient signal-to-noise ratio and stability, 10-20 exposures are generally carried out continuously. In addition, because the brightness of the sky changes very quickly during shooting, the adjustment amount of the exposure time is large, certain technical difficulty exists, and certain operation skill level is required.

Dome flat field shooting is not influenced by the brightness of sky light and weather, can shoot at any time, but the homogeneity to the light source, the scattering homogeneity of flat field screen etc. require highly. One benefit of a dome flat field is that a very high signal-to-noise ratio can be achieved in a very short time (typically on the order of seconds). One disadvantage, however, is that the illumination of the light source, no matter how uniform it is, differs somewhat from the case of the flat field of sky light and of real shots, so that illumination correction is required for the dome flat field.

Step 1.2) observing the FGK type fixed star to be detected by using a telescope;

v is used in the observation_SAGERespectively observing the wave band and the g/i wave band;

firstly, before observation, the special design of the invention is installedv_SAGEA band filter, and a g/i band filter.

The telescope is kept pointing too far away from the zenith during observation (the air mass must not be too large, generally less than 1.5 is recommended) to ensure that atmospheric extinction is not too severe.

The exposure time is also appropriate during observation, and on the one hand it cannot be too short, otherwise there will be a shutter effect (typically 1-2 seconds), and it cannot be too long, otherwise the star image will saturate.

The point spread function PSF outline of the star image needs to be checked in real time, the fact that the star image is not elongated and virtual focus cannot occur is guaranteed, if the star image is elongated, whether a tracking system has problems or not needs to be checked, and maintenance is conducted in time. The circularity (elongation) of the star image can be generally determined by the following formula.

The Roundness (Roundness) is used to determine the degree of star image circle and is defined as

Wherein h is_xAnd h_yThe full width at half maximum FWHM, which is a one-dimensional Gaussian fit in the x and y directions, respectively, is typically [ -1.0,1.0]It is clear that for a constant star image, the more circular the range is closer to 0.

And if the star image has virtual focus, focusing is carried out until the star image is sharp. The sharpness of the star image can be generally judged by the following formula.

Sharpness (Sharpness) requires upper and lower limits to be given, defined as

Wherein DN_maxIs the maximum reading number, DN, in the star image_neiIs the average of the surrounding neighboring pixels and h is the full width at half maximum FWHM of the two-dimensional gaussian fit. General defaults for this parameter are taken to [0.2, 1.0%]And (3) a range.

Step 1.3) combining background images, carrying out background correction on observation images of all to-be-detected FGK type stars, and eliminating bias voltage and non-uniformity influences of a detector and photoelectric observation equipment;

background changes may occur several or even more than ten ADUs a night, so shots are taken before and after the observation (typically 5-10 shots each), and then the background images before and after the observation are combined.

For the observed star image to be detected, the combined background image at the later time is subtracted.

comprises the following specific steps

Firstly, for each dark field, background correction is needed, namely the background image combined in the step 1.3) is subtracted from the dark field; because the dark field is weak, the dark field is generally shot for a long time, such as several hours, so that the dark field cannot be submerged in instrument noise; therefore, for the dark field correction of the final photometric image of the star, the dark field time needs to be reduced to the exposure time observed by the star; and then dark field correction is carried out on the actual observation image, and specifically, dark current in the exposure time of the corresponding star is reduced.

the method comprises the following specific steps:

first for different bands (v)_SAGEThe flat field of the/g/i wave band) needs to be processed separately, the background correction is carried out respectively, and the background image combined in the step 1.3) is subtracted.

And correcting a dark field to reduce dark current, and specifically referring to step 1.4).

Because the multiple flat fields of different wave bands need to be visually checked, the condition that no bad image exists is ensured, the flow is stable, then the different wave bands are respectively combined, and finally normalization is carried out.

For the flat field shot by the flat field of the sky light, if the flow rate of each frame is obviously different, normalization is needed, and then combination is carried out to obtain the final flat field.

Step 1.6) v-treatment of fixed stars to be tested_SAGEMeasuring light of the wave band and g/i wave band observation images;

for a star, which can be generally regarded as a point source, the signal-to-noise ratio of the star image can be calculated by the following formula:

wherein DN is CCD reading, Gain is Gain, and flux is flow. flux_totalAnd flux_backgroundRepresenting the total and background daylight flux, respectively; DN_totalAnd DN_backgroundCCD readings representing total and background daylight, respectively.

The method is characterized in that Full Width Half Maximum (FWHM) fitting is carried out on a star image so as to judge and estimate the size of a photometric aperture, and the FWHM which is 1.5-2 times the full width half maximum is generally taken as a proper photometric aperture (the innermost circle of fig. 3), so that the balance can be carried out in the process of collecting signal energy and reducing background noise as much as possible so as to obtain an optimal value.

Reasonable values for the background fit take FWHM of 4-5 times and 6-7 times as the inner and outer radii (middle and outermost circles in fig. 3), which can represent the background of the sky near the stars and is not affected by the stars and stars.

The principle of aperture photometry is to calculate the total number of photons in the photometry aperture and then subtract the corresponding celestial light background (the range between the two green circles in fig. 3 is estimated), so that the obtained flux is the flux of the starlight, and the logarithm is taken to obtain the corresponding instrument star, etc. Generally, the current mature software such as IRAF (http:// IRAF. noao. edu /) or SExtractor (http:// www.astromatic.net/software/sexfractor) can perform batch aperture photometry.

For aperture photometry, aperture correction is also required to obtain the full flow. This requires a growth curve, i.e. in the image, a typical batch of unsaturated stars is selected to be measured with a series of aperture sizes, so that the number of collected photons can be seen to be larger and larger as the aperture increases, and then approaches a constant.

FIG. 4 is a typical correction of the growth curve. The method comprises the steps of selecting more than 20 unsaturated bright stars from the same image to perform multi-aperture photometry, selecting 16 photometric apertures with photometric radius r being 5-35 pixels to perform aperture photometry, and then taking a median value of the star equal differences of all the stars at each aperture (the star equal of the aperture-the star equal of the instrument without flow loss), wherein a median line at each aperture is a growth curve of the star image of the image.

Step two: observing and processing flow standard star

Preferably, the steps specifically include:

step 2.1) v-flow Standard Star_SAGEObserving a wave band and a g/i wave band;

during observation, light measuring night is selected, and the atmosphere is stable all night and is at a cloudy night.

This step can be referred to as step 1.2).

Before observation, v specially designed according to the invention is installed_SAGEA band filter, and a g/i band filter.

The point spread function PSF outline of the star image needs to be checked in real time, the fact that the star image is not elongated and virtual focus cannot occur is guaranteed, if the star image is elongated, whether a tracking system has problems or not needs to be checked, and maintenance is conducted in time.

The observation standards are uniformly distributed at different atmospheric masses (typically between 1-2),

step 2.2) v-flow Standard Star_SAGECorrecting background, dark field and flat field of observation images of wave bands and g/i wave bands;

step 2.3) v-flow Standard Star_SAGEPhotometry is carried out on the images of the wave bands and the g/i wave bands, so that instrument stars and the like are obtained;

this step can be referred to as step 1.6).

The Full Width Half Maximum (FWHM) of the star image is fitted to judge and estimate the size of the photometric aperture, and generally 1.5-2 times of the Full Width Half Maximum (FWHM) is taken as a proper photometric aperture (the innermost circle of fig. 3), so that the balance can be carried out in collecting signal energy and reducing background noise as much as possible, and an optimal value is obtained.

The principle of aperture photometry is to calculate the total number of photons in the photometry aperture, and then subtract the corresponding celestial light background (the range between the middle circle and the outermost circle of fig. 3 is estimated), so the obtained flux is the flux of the starlight, and the logarithm is taken to obtain the corresponding instrument star, etc. Generally, the current mature software such as IRAF (http:// IRAF. noao. edu /) or SExtractor (http:// www.astromatic.net/software/sexfractor) can perform batch aperture photometry.

Step three: fitting atmospheric extinction curve and calibrating flow of fixed star to be measured

Preferably, the steps specifically include:

calculation formula of atmospheric mass:

v_cali-v_inst＝k_0,v+k_1,vχ+k_2,v(v_cali-g_cali) (4)

g_cali-g_inst＝k_0,g+k_1,gχ+k_2,g(g_cali-i_cali) (5)

i_cali-i_inst＝k_0,i+k_1,iχ+k_2,i(g_cali-i_cali) (6)

χ＝sec z (7)

wherein z is the zenith angle, the formula is applicable to the range of zenith angles z <60 ° -75 °, which is the range in which typical astronomical observations are made.

Multiple wavelength by photometry (v)_SAGE/g/i) observing standard stars and fitting the extinction curve to perform flow calibration on star observation data at the later time.

FIG. 5 is a fitted v_SAGEThe method comprises the steps of fitting a main extinction coefficient and a 1-level extinction coefficient, iterating obtained results into a formula, and solving to obtain a final extinction coefficient, wherein a wave band atmospheric extinction curve is formed, a Y axis is the star equal difference between an instrument star and the like and a real star outside the atmosphere, an X axis is the atmospheric quality of a standard star, and the coefficients of color items in the formulas (4) - (6) are very small and can be ignored under the general condition.

Step 3.2) utilizing an atmospheric extinction curve to carry out flow calibration on the fixed star to be detected;

v of FGK type star to be measured_SAGEAnd (4) bringing the instrument stars and the like in the/g/i wave band into the atmosphere extinction curve obtained by fitting, thereby obtaining calibration stars and the like outside the atmosphere.

For each waveSection of instrument stars, or the like, to be brought into the atmospheric extinction curve of the corresponding band, e.g. v_SAGEThe star of the instrument of the wave band is to be brought into v_SAGEAnd obtaining an atmospheric extinction curve of the wave band, thereby obtaining an atmospheric extraterrestrial star and the like, namely a calibrated star and the like.

Step four: pair of "(v)_SAGE-g) - (g-i) color-to-metal abundance relationship [ Fe/H]"fitting to

Preferably, the steps specifically include:

kurucz 1993 sidereal atmosphere model ATLAS

Html is a good star atmosphere model library, and 7600 samples of star types (O3V-M2I types) are included in the library, wherein star atmospheric parameters range is large, and T is T_eff3500 and 50000K; log g 0.0 to +5.0, step size + 0.5; [ Fe/H ]]The response curve of the spectrum convolution filter of the model is used for obtaining corresponding stars and the like, wherein the response curve of the spectrum convolution filter of the model corresponds to +1.0, +0.5, +0.3, +0.2, +0.1, +0.0, -0.1, -0.2, -0.3, -0.5, -1.0, -1.5, -2.0, -2.5, -3.0, -3.5, -4.0, -4.5 and-5.0, and the spectrum of the star atmosphere parameters (the wavelength covers from 100nm ultraviolet band to 10 mu m infrared band) is provided.

The convolution formula for the Vega system is as follows:

MAG_Vega(Obj)＝-2.5log(∫{F_l(Obj)S_λdλ}/∫{F_l(Vega)S_λdλ}) (8)

MAG_Vega(Obj)＝-2.5log(∫{F_ν(Obj)S_νdν}/∫{F_ν(Vega)S_νdν}) (9)

the convolution formula for the AB system is as follows:

MAG_AB(Obj)＝-2.5log(∫{F_ν(Obj)S_νdν}/∫{S_νdν})-48.6 (10)

where λ is the wavelength, v is the frequency, F_ν(Obj) is the flow of the celestial body in ergs^-1cm^-2Hz^-1，S_νIs instrumentCorresponding curve of the device, F_ν(Vega) is the flow rate of Neisseria hernalis in ergs^-1cm^-2Hz^-1。

Therefore, we can obtain v of the star by convolving Kuruccz star atmosphere model by the above formula_SAGEThe star of the/g/i wave band, and the like, and each spectrum corresponds to a known star atmospheric parameter (T)_eff,log g,[Fe/H]). Since we only need model spectra and atmospheric parameters of FGK type stars, the main parameter range is limited to the effective temperature T_eff3500 and 7250K.

Step 4.2) fitting Kurucz fixed star atmosphere model (v)_SAGE-g) - (g-i) colour-metal abundance [ Fe/H]The relationship of (1);

FIG. 6 shows the Kurucz model log 4.5, effective temperature T _eff4500-_SAGE-g) - (g-i) colour-metal abundance [ Fe/H]The relationship (2) of (c).

In order to limit FGK type stars, the effective temperature T of the model spectrum is selected_effBetween 3500 and 7250K, consider the surface gravity log g of 2-5. From fig. 6 it can be seen that log 4.5, the effective temperature T_effMetal abundance sum (v) in case of 4500-_SAGEThere is a good monotonic correlation between colors-g) - (g-i). If more detailed information is known, such as the determined effective temperature T_effAnd the surface gravity log g, the correlation is better, and the obtained metal abundance precision is higher and can reach 0.1-0.2dex.

Step five: method for calculating metal abundance of fixed star to be measured by photometry

Preferably, the steps specifically include:

it can be seen from fig. 6 that the results obtained have a large dispersion if the spectral patterns are not distinguished. However, if more detailed spectral patterns can be distinguished, even log g can be determined, the resulting accuracy will be high, up to [ Fe/H ] -0.1-0.2 dex.

And 5.2) sorting the obtained metal abundance results of the FGK type stars to be detected, and generating a table with a fixed format according to the requirements of users.

V of the invention_SAGEWave band filter for measuring CaII H of fixed star&The K absorption line can accurately reflect the metal abundance of the fixed star; by measured v_SAGE(v) obtained by fitting the colors of the waveband star and the like and other adjacent wavebands (such as g/i waveband) by using a Kurucz star atmosphere model_SAGE-g) - (g-i) color [ Fe/H-]The relation can obtain the metal abundance [ Fe/H ] of the fixed star to be detected](ii) a The method is simple to operate, time can be greatly saved in observation, the advantage of photometry can be played, all FGK fixed stars in a view field can be measured at one time, and the measuring efficiency is greatly improved.

While several embodiments of the present invention have been presented herein, it will be appreciated by those skilled in the art that changes may be made to the embodiments herein without departing from the spirit of the invention. The above examples are merely illustrative and should not be taken as limiting the scope of the invention.

Claims

1. A method for measuring the abundance of FGK-type sidereal metals, which is characterized by comprising the following steps:

firstly, observing and processing data of FGK type fixed stars to be detected; when observing the FGK type fixed star to be measured, the filter v for effectively measuring the metal abundance of the FGK type fixed star is adopted_SAGEThe filter v_SAGEThe central wavelength is 395nm, and the bandwidth of the optical filter is 29 nm;

observing and processing the flow standard star;

fitting an atmospheric extinction curve, and calibrating the flow of the fixed star to be measured;

step five, solving the metal abundance of the fixed star to be detected by a photometric method;

wherein:

the first step specifically comprises the following steps:

step 1.6) v-treatment of fixed stars to be tested_SAGEPhotometry of observation images of wave bands and g/i wave bands;

the second step specifically comprises:

step 2.1) v-flow Standard Star_SAGEObserving the wave band and the g/i wave band, wherein the observation needs to be performed at a photometric night, and the atmosphere is stable and cloudless at night; controlling exposure time, and checking the point spread function PSF outline of the star image in real time to ensure that the star image is not elongated and has no virtual focus;

step 2.3) v-flow Standard Star_SAGEPhotometry is carried out on the images of the wave bands and the g/i wave bands to obtain instrument stars and the like;

the third step specifically comprises:

calculation formula of atmospheric mass:

v_cali-v_inst＝k_0,v+k_1,vχ+k_2,v(v_cali-g_cali) (4)

g_cali-g_inst＝k_0,g+k_1,gχ+k_2,g(g_cali-i_cali) (5)

i_cali-i_inst＝k_0,i+k_1,iχ+k_2,i(g_cali-i_cali) (6)

χ＝sec z (7)

v of FGK type star to be measured_SAGEBringing instrument stars and the like of the/g/i wave band into the atmospheric extinction curve obtained in the step 3.1) by fitting to obtain calibration stars and the like outside the atmosphere; bringing the instrument star and the like of each wave band into an atmospheric extinction curve of the corresponding wave band;

the fourth step specifically comprises:

step 4.1) selecting FGK type constellations from Kurucz star atmospheric model and convolving the samples to obtain v_SAGEA/g/i band star, etc.;

the fifth step specifically comprises:

step 5.1) scaling the observations_SAGEObtained by fitting star-to-star substitution of/g/i waveband FGK type star(v_SAGE-g) - (g-i) colour-metal abundance [ Fe/H]Correlating to obtain the metal abundance of the metal;

2. The method of claim 1, wherein in step 4.1), the v of stars is obtained by convolving the Kuruccz star atmosphere model with the following formula_SAGEThe/g/i wave band star is equal:

the convolution formula for the Vega system is as follows:

MAG_Vega(Obj)＝-2.5log(∫{F_l(Obj)S_λdλ}/∫{F_l(Vega)S_λdλ}) (8)

MAG_Vega(Obj)＝-2.5log(∫{F_ν(Obj)S_νdν}/∫{F_ν(Vega)S_νdν}) (9)

the convolution formula for the AB system is as follows:

MAG_AB(Obj)＝-2.5log(∫{F_ν(Obj)S_νdν}/∫{S_νdν})-48.6 (10)

where λ is the wavelength, v is the frequency, F_ν(Obj) is the flow rate of the stars, in ergs^-1cm^-2Hz^-1，S_νIs the corresponding curve of the instrument, F_ν(Vega) is the flow rate of Neisseria hernalis in ergs^-1cm^-2Hz^-1。