# How to calculate B-V colour index value percentage difference

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I need to calculate a percentage difference of a B-V colour index between its estimated and actual value. So I tried doing this by difference between values/actual value x 100. However as B-V values can be on either side of zero this did not give representative answers.

So if anyone knows a way of calculating percentages of values close to zero or on either side of zero their help would be appreciated.

Thanks

$B-V$ corresponds to the base 10 logarithm of a flux ratio.

$$B-V = -2.5 log left(frac{f_B}{f_V} ight)$$

So trying to guess what you are trying to calculate, it is the percentage change in the blue to visible flux ratio?

In which case the percentage change is $$p = frac{ 10^{-(B-V)_2/2.5} - 10^{-(B-V)_1/2.5}}{10^{-(B-V)_1/2.5}} imes 100$$

A percentage change can of course be negative.

## How to calculate B-V colour index value percentage difference - Astronomy

The section on Radiation Laws indicated that there is a relationship between the temperature of a blackbody and the location of the peak in the radiation distribution as a function of wavelength (Wien Law) . This allows definition of some continuous quantities called color indices that can be determined directly from observations and that are indirect indicators of temperature for a star.

### Astronomical Color Filters

Optical devices called filters may be devised that allow light to pass in a limited range of wavelengths. In astronomy, a variety of filters are used to emphasize light in a particular wavelength region, but the most common are called the U (ultraviolet), B (blue), and photovisual (V) filters. Their transmission of light as a function of wavelength, as well as the response of the average human eye, is illustrated in the following figure.
 Response of standard astronomical filters and the human eye

The names for the filters arise because the peaks for transmission for the U, B, and V filters are in the ultraviolet, blue, and yellow-green region of the spectrum (the human eye is most sensitive to the yellow-green region of the visible-light spectrum). Thus, astronomers can measure the intensity of light from a source like a star in each of these regions of the spectrum by passing the light collected by the telescope through the appropriate filter.

(Note that for convenience in plotting these distributions have been normalized to unity at the respective peaks by the Stefan-Boltzmann Law, the area under the peak for the hot star Spica is in reality 2094 times the area under the peak for the cool star Antares.)

### Color Index Examples

Generally, the negative values of these color indices are an indication that Spica is a hot star, with most of its radiation coming at shorter wavelengths. On the other hand, for Antares B = 2.7 and V=0.9, and the B - V color index is

The positive value of B - V in this case is an indication that Antares is a cool star, with most of its radiation coming at longer wavelengths.

## Colour index

Our editors will review what you’ve submitted and determine whether to revise the article.

Colour index, in astronomy, the difference between two measurements of the magnitude (brightness on a logarithmic scale) of a star made at different wavelengths, the value found at the longer wavelength being subtracted from that found at the shorter. Usually the two wavelengths are the blue (B) and the visual (V) as defined in the UBV system.The index is a measure of a star’s colour, an indication of its temperature, and a fairly crude description of the distribution of its radiated energy through the electromagnetic spectrum. The zero point of the colour index scale in the UBV system is chosen such that stars that have a surface temperature of 7,400 K and that are white in colour, such as Vega, have a colour index of zero. Hot, blue stars have negative colour indices, as they radiate most strongly and therefore have numerically lower magnitudes at short wavelengths, and those of cool, red stars are positive. The colour index of a star is increased by the passage of its light through interstellar matter the amount by which it exceeds the normal value for its spectral type is called the colour excess. (See also magnitude and UBV system.)

This article was most recently revised and updated by Erik Gregersen, Senior Editor.

## API documentation (Ramirez2005)¶

Relation between effective temperature and color given by Ramirez and Melendez 2005.

Ramirez and Melendez 2015, ApJ 626, 465-485 (please not that Ramirez has a non-ASCII accent on the i and Melendez an accent on the second e) give a relation between the stellar effective temperature and the color concerning various bands. This class allows to carry out the conversion in both directions.

 availableBands () Get a list of available band identifiers. colorToTeff (band, X, feH[, stype, ignoreRange]) Converts color into effective temperature according to Eq. colorToTeff_nop (band, X, feH[, stype]) Converts color into effective temperature according to Eq. teffToColor (band, teff, feH[, stype, dteff, …]) Converts effective temperature into color according to Eq. teffToColor_nop (band, teff, feH[, stype, …]) Converts effective temperature into color according to Eq.
_checkBand ( band ) ¶

Check whether band identifier is valid.

Check whether stellar type (main-sequence/giant) is valid.

Convert band name used in tables to internal representation.

Identifier used in the class.

Extract lines pertaining to specified table.

tableno : int

Number of the table to be extracted.

Part of the file belonging to the specified table.

tableno : int

Number of the table to be extracted.

IDs of all bands in the table.

result : array

tableno : int

Number of the table to be extracted.

Determine where to find coefficients for given metallicity in Tables 4 and 5.

Get a list of available band identifiers.

All strings used to identify bands.

Converts color into effective temperature according to Eq. 2.

This method takes the polynomial correction into account. Note that no interpolation is implemented between the polynomials defined in Tables 4 and 5, but the appropriate polynomial (according to footnote (a) on under the tables) is used.

The color index (e.g., value of B-V).

feH : float

stype : string,

Type of star (main sequence or giant).

ignoreRange : boolean, optional

If True, the validity range of the relations will be ignored. Otherwise (default) an exception will be raised when a value outside the range is encountered.

The effective temperature in K.

Converts color into effective temperature according to Eq. 1.

The conversion using to Eq. 1 neglects a polynomial correction for metallicity. According to RM05, this causes a systematic error on the order of ‘30 or 40 K’.

The color index (e.g., value of B-V).

feH : float

stype : string,

Type of star (main sequence or giant).

The effective temperature in K.

Converts effective temperature into color according to Eq. 2.

This method inverts Eq. 2 using an iterative scheme.

teff : float

Effective temperature in K.

feH : float

stype : string, , optional

Type of star (main sequence or giant).

dteff : float, optional

Temperature difference to be reached by the iteration [K]. Default is 0.01.

maxiter : int, optional

The maximum number of iterations to be carried out. Default is 100.

Color in the specified band.

Converts effective temperature into color according to Eq. 1.

This method inverts Eq. 1. Note that the equation is parabolic in the color (i.e., X). Therefore, there are two solutions of which the one falling within the validity ranges specified in Tables 4 and 5 of RM05 is selected. If none or both of the solutions are valid, an exception is raised.

teff : float

Effective temperature in K.

feH : float

stype : string,

Type of star (main sequence or giant).

noRaise : boolean, optional

If True, no exceptions will be raised, but warnings will be given Both candidate solutions will be returned in this case.

Color in the specified band.

## How to calculate B-V colour index value percentage difference - Astronomy

Dust grains in the interstellar medium have a typical size that is comparable to the wavelength of blue light. The result is that the blue light coming from distant objects is strongly absorbed and scattered by the dust, essentially removing it from the light reaching us and making the objects appear redder than they really are. This is known as interstellar reddening and must be taken into account by astronomers analysing data taken at optical wavelengths in particular.

The reddening of an object is inversely proportional to the wavelength of optical light, so shorter wavelengths (blue) are more heavily reddened than longer (red) wavelengths. We can determine the degree of reddening by measuring the colour index (B-V) of the object and comparing that to its true colour index (B-V)0 through the equation:

Since both interstellar reddening and extinction are the result of the interaction of starlight with dust grains, they are inextricably linked and we should expect that the more dust along the line of sight, the more pronounced the reddening and the higher the extinction. This is indeed what is found, with extinction and reddening linked by the equation:

where AV is the extinction measured in the V band.
To calculate the correct distance (in parsecs) to an object taking into account extinction, we must expand the distance equation to be:

d = 10 0.2(m-M+5-AV)

By subtracting the extinction in the exponent of this equation, we are brightening the magnitude to account for loss of light.

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All material is © Swinburne University of Technology except where indicated.

## Question : An amateur astronomer is researching statistical properties of known stars using a variety of databases. She collects the color index, or B−V index, and distance (in light years) from Earth for 10 stars. The color index of a star is the difference in the light absorption measured from the star using two different light filters (a B and a V filter). This then

An amateur astronomer is researching statistical properties of known stars using a variety of databases. She collects the color index, or B−V index, and distance (in light years) from Earth for 10 stars. The color index of a star is the difference in the light absorption measured from the star using two different light filters (a B and a V filter). This then allows the scientist to know the star's temperature. A negative value means a hot blue star. A light year is the distance light can travel in 1 year, which is approximately 5.9 trillion miles. The stellar data is reproduced in the table below. Calculate the correlation coefficient r using a TI-83, TI-83 plus, or TI-84 graphing calculator (round your answer to two decimal places).

"﻿B−V index" Distance (ly)
1.03 142.6
-0.02 1138.8
0.36 428.6
0.91 1153.4
1.04 647.6
0.47 301.7
0.08 741.4
1.49 794.8
1.08 918.8
1.14 644.6

To better grasp the different temperatures of stars it should be noted that 1 Kelvin equals to -272.15 degrees Celsius. To convert Kelvin to Celsius, use the following simple formula: 1K – 273.15 = -272.15 °C (the value 273.15 is a constant).

The current classification system uses the letters O, B, A, F, G, K, and M, to sequence stars from the hottest to the coolest. Overall there are 7 spectral classes:

• O Class (blue) – These are very hot stars, with surface temperatures above 30,000 Kelvin.
• B Class (gradient between blue and white) – In this group, temperatures are between 30,000 Kelvin and 10,000 Kelvin.
• A Class (white) – Temperatures are between 10,000 Kelvin to 7,500 Kelvin.
• F Class (gradient between white and yellow) – These stars are between 7,500 Kelvin to 6,000 Kelvin.
• G Class (yellow) – Temperatures between 6,000 K to 5,000 K. This class includes our Sun.
• K Class (orange) – In this group of stars the temperatures are between 5,000 Kelvin and 3,500 Kelvin.
• M Class (red) – The stars in this class are the coldest, with surface temperatures below 3,500 Kelvin.

To distinguish between giant stars and dwarfs, the Morgan–Keenan (MK) luminosity class is appended to the Harvard classification for the star. Luminosity values are based on the width of certain absorption lines in the star’s spectrum which vary with the density of the atmosphere.

## Tuesday, 12 February 2013

### Exoplanet - Is there any way a planet could form independent of a star?

Well you need to see the related question brown dwarfs and planets , because the answer to your question depends on how you define a planet.

If you demand that a "planet" has a rocky core then it seems very unlikely that a planet could form in isolation away from a parent star. The parent star is needed in order to differentiate the rocky material from the gas and allow it to condense.

On the other hand, if you wish to define a planet as simply an object below a certain mass (say the deuterium burning threshold at 13 Jupiter masses) then it seems very likely that such an object could form in isolation. They would be entirely gaseous, but there would be little to distinguish them from brown dwarfs at only slightly higher masses.

At present there are plenty of candidate "free-floating planetary mass" objects.
For example see Joergens et al. (2014) Liu et al. (2013) Zapatero-Osorio et al. (2000). Unless we have our understanding of the physics completely wrong, then it is likely that at least some of these are lower than 13 Jupiter masses. However, their origin remains unclear. It is possible they could all have formed around stars and then subsequently been ejected, but the presence of significant numbers of these objects in young star forming regions and the lack of $sim$10 Jupiter-mass objects orbiting stars, suggests that there is an alternative formation scenario that can produce such objects in isolation.

What could these formation scenarios be? These low-mass objects could just be an extension to lower masses of the fragementation process that forms stars they could be ejected embryos that started their lives in multiple systems they could be "failed" stellar cores that could not accrete more gas because of photoevaporation by nearby massive stars or they could form by gravitational instability around stars with unusually massive disks and be ejected by a close encounter with another star. These possibilities are reviewed by Whitworth et al. (2006) and Chabrier et al. (2014), and are all still thought plausible to some extent.

## How to calculate B-V colour index value percentage difference - Astronomy

Astronomy Laboratory Observation

Spectral Classification of Stars

In this exercise we will obtain a spectral classification of some of the stars which were studied in the Photoelectric Photometry observation, scheduled earlier. If you have not completed that exercise you must do so before proceeding with this one. Obtain your data taken during the Photometry exercise from your resourceful instructor.

1. Log into the Carson-Newman computer network at a Windows computer (for example, in DSC 126). Double click on the Network Applications Shortcuts icon, on the Astronomy icon, then on the icon for Stellar Spectra. Click on the Login option at the top of the screen. Enter your name on the first line. Click "OK."

2. Under the Run menu, click Take Spectra . Open the dome and turn on the tracking.

3. Select one of the stars from your photometry data. You should eventually include one of your reddest stars (with a larger value of MB-V), one of the bluest stars and two more or less equally spaced in between.

Click the Set Coordinates button and enter the coordinates of the star you have selected. After you have completed entering the coordinates, that star should be in the center of your field of view. If necessary, click the monitor button, to change your view to the instrument. If needed, slew the telescope until the star is in the center of the spectrometer slit.

4. Click Take Reading then Start/Resume count and observe the spectrum as it builds up on your screen. When the signal/noise ratio reaches 100, click Stop Count. (For a faint star, the program may stop early, which is OK.) Click Save and enter the last three digits of the Object identification number in the box for the ID of the star. (Enter a sequence number, like 001 or 002, if no Object identification number is displayed.) Notice that the file name for the saved spectrum includes your name followed by these three digits. Record this file name in the data table on the next page. Also record the file name in the margin beside the data for this star, on the photometry data sheet.

5. Click Return and repeat steps 3 and 4 for a different star. Continue until four different stellar spectra have been stored.

6. After all spectra have been stored, click Run at the top of the main screen of the program, then click Classify Spectra. Click Load then click Atlas of Standard Spectra, select Main Sequence and click OK. Turn on the Difference option. The smaller window, with several main sequence spectra displayed, may be moved aside, closed, or minimized, so that the main screen of the Classify Spectra program can be seen.

7. Click Load - Unknown Spectrum - Saved Spectra and then select one of your stored spectrum files, as recorded in your data table. Click OK and observe that a standard mainsequence spectrum is plotted at the top, your saved spectrum in the middle, and the difference between them in the bottom panel. Click the Down and/or Up buttons and notice how the difference plot changes as different standard spectra are compared with yours. If you happen to have a spectrum which exactly matches one of the standards, then the difference will be fairly flat. If not, then a standard on one side will have a few small peaks, while the one on the other side will have peaks pointing the opposite way. You should be able to estimate the correct spectral classification, according to the relative sizes of the difference peaks for the two adjacent standard spectra. For example, if the difference peaks for A1 are about 3 times as pronounced as for A5, then your spectrum is closer to A5 than A1, so A4 would be a good estimate for the spectral classification. If the difference peaks for A1 and A5 were about the same magnitude and opposite, then half-way between, or A3 would be a good estimate. Note that, for example, F0 immediately follows A9 in this scheme. Thus, if your spectrum is between A5 and F0, you could think of F0 as equivalent to "A10" as you try to classify your spectrum.

8. Record the classification of the spectrum in the table below, beside the appropriate filename. Also record the color index, which is the corresponding value of MB-V recorded in your photometry data table. Use the conversion table below to convert the spectral classification to the corresponding value of the color index. Record this value and calculate the deviation between the two values. If the photometric value is a little larger than the spectroscopic value, that would indicate that the star appears a little redder than it should. Can you give a reason why this might be the case?

## HIPPARCOS - Hipparcos Main Catalog

Each of the catalogues contains a large quantity of very high quality astrometric and photometric data. In addition there are associated annexes featuring variability and double/multiple star data, and solar system astrometric and photometric measurements. In the case of the Hipparcos Catalogue, the principal parts are provided in both printed and machine-readable form (on CDROM). In the case of the Tycho Catalogue, results are provided in machine-readable form only (on CDROM). Although in general only the final reduced and calibrated astrometric and photometric data are provided, some auxiliary files containing results from intermediate stages of the data processing, of relevance for the more-specialised user, have also been retained for publication. (Some, but not all, data files are available from the Centre de Donnees astronomiques de Strasbourg.)

The global data analysis tasks, proceeding from nearly 1000 Gbit of raw satellite data to the final catalogues, was a lengthy and complex process, and was undertaken by the NDAC and FAST Consortia, together responsible for the production of the Hipparcos Catalogue, and the Tycho Consortium, responsible for the production of the Tycho Catalogue. A fourth scientific consortium, the INCA Consortium, was responsible for the construction of the Hipparcos observing programme, compiling the best-available data for the selected stars before launch into the Hipparcos Input Catalogue. The production of the Hipparcos and Tycho Catalogues marks the formal end of the involvement in the mission by the European Space Agency and the four scientific consortia.

### Parameters

Name
Name of the star in the recommended format for Hipparcos stars, as created by concatenating the prefix 'HIP ' and the Hip_Number identifier in the original catalog. Entries in the Hipparcos (HIP) Catalog have exactly the same identifier as in the Hipparcos Input Catalog (HIC), notice.

RA
Right ascension in the specified equinox for epoch J1991.25. This was given in the ICRS reference system (J2000 equator) in the original Hipparcos Catalog, and thus equinox 2000 should be specified to avoid inaccuracies due to the non-rigorous HEASARC coordinate precession algorithm. This parameter was given to a truncated precision of 0.01 seconds of time in the original Hipparcos Catalog. If the 'precise' RA is desired, one should use the value of the parameter RA_deg which contains the complete RA in decimal degrees.

Dec
Declination in specified equinox for epoch J1991.25. This was given in the ICRS reference system (J2000 equator) in the original Hipparcos Catalog, and thus equinox 2000 should be specified to avoid inaccuracies due to the non-rigorous HEASARC coordinate precession algorithm. This parameter was given to a truncated precision of 0.1 arcseconds in the original Hipparcos Catalog. If the 'precise' declination is desired, one should use the value of the parameter Dec_deg which contains the complete declination in decimal degrees.

HIP_Number
The Hipparcos Catalog running number, which is the same as the that in the Hipparcos Input Catalog. The star entries are, with a few exceptions, ordered by increasing HIP number, which basically follows the order of the object's right ascension (Equinox J2000) independent of declination.

Prox_10asec
A proximity flag which provides a coarse indication of the presence of nearby objects within 10 arcseconds of the position of the given star. If non-blank, it indicates that there are one or more distinct Hipparcos ('H') or Tycho ('T') Catalog entries if both 'H' and 'T' apply, then 'H' is the adopted value, notice.

Vmag
The magnitude in Johnson V band, given to a precision of 0.01 magnitudes in the original Hipparcos Catalog.

Var_Flag
A coarse variability flag which indicates if the entry (or one of the components in the case of a multiple system) is variable in its Hipparcos magnitude Hip_mag at the level of:

Vmag_Source
The source of the V magnitude:

RA_Deg
The right ascension expressed in degrees for epoch J1991.25 (JD2448349.0625 (TT)) in the ICRS (International Celestial Reference System, consistent with J2000) reference system, and given to a precision of 10 -8 degrees in the original Hipparcos Catalog. There are 263 cases where these fields are missing (no astrometric solution could be found).

Dec_Deg
The declination expressed in degrees for epoch J1991.25 (JD2448349.0625 (TT)) in the ICRS (International Celestial Reference System, consistent with J2000) reference system, and given to a precision of 10 -8 degrees in the original Hipparcos Catalog. There are 263 cases where these fields are missing (no astrometric solution could be found)

Astrom_Ref_Dbl
Reference flag for astrometric parameters of double and multiple systems. This flag indicates that the astrometric parameters refer to:

Parallax
The trigonometric parallax pi in units of milliarcseconds: thus to calculate the distance D in parsecs, D = 1000/pi. The estimated parallax is given for every star, even if it appears to be insignificant or negative.

PM_RA
The proper motion component in the RA direction expressed in milliarcseconds per Julian year (mas/yr), and given with respect to the ICRS reference system: mu_RA* = mu_RA x cos (declination).

PM_Dec
The proper motion component in the declination direction expressed in milliarcseconds per Julian year (mas/yr), and given with respect to the ICRS reference system.

RA_Error
The standard error in the Right Ascension given at the catalog epoch, J1991.25, and expressed in milliarcseconds: sigma_RA* = sigma_RA x cos (declination).

Dec_Error
The standard error in the declination given at the catalog epoch, J1991.25, and expressed in milliarcseconds.

Parallax_Error
The standard error in the parallax given in milliarcseconds.

PM_RA_Error
The standard error in the proper motion component in the RA direction expressed in milliarcseconds per Julian year (mas/yr): sigma_mu_RA* = sigma_mu_RA x cos (declination).

PM_Dec_Error
The standard error in the proper motion component in the declination direction expressed in milliarcseconds per Julian year (mas/yr), sigma_mu_declination.

Crl_Dec_RA
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (declination over RA).

Crl_Plx_RA
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (parallax over RA).

Crl_Plx_Dec
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (parallax over declination).

Crl_Pmra_RA
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (proper motion in RA over RA).

Crl_Pmra_Dec
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (proper motion in RA over declination).

Crl_Pmra_Plx
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (proper motion in RA over parallax).

Crl_Pmdec_RA
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (proper motion in declination over RA).

Crl_Pmdec_Dec
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (proper motion in declination over declination).

Crl_Pmdec_Plx
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (proper motion in declination over parallax).

Crl_Pmdec_Pmra
The correlation coefficient expressed as a real numerical value (in the printed catalog this is expressed in per cent, notice): (proper motion in declination over proper motion in RA).

Reject_Percent
The percentage of data that had to be rejected in order to obtain an acceptable solution.

Quality_Fit
The goodness-of-fit statistic: this number indicates the goodness of fit of the astrometric solution to the accepted data (i.e., excluding the rejected data). For good fits, this should approximately follow a normal distribution with zero mean value and unit standard deviation. Values exceeding, say +3, thus indicate a bad fit to the data.

BT_Mag
The mean magnitude in the Tycho photometric system, B_T.

BT_Mag_Error
The standard error of the B_T magnitude, BT_mag.

VT_Mag
The mean magnitude in the Tycho photometric system, V_T.

VT_Mag_Error
The standard error of the V_T magnitude, VT_mag.

BT_Mag_Ref_Dbl
a reference flag for BT_mag and VT_mag which indicates, for non-single stars, the component measured in Tycho photometry, or indicates that several components have been directly measured together by Tycho, or have had their Tycho data combined. The flag takes the following values:

BV_Color
The (B-V) color index in, or reduced to, the Johnson UBV system.

BV_Color_Error
The standard error of the (B-V) color index, BV_Color.

BV_Mag_Source
The source of the (B-V) color index, BV_Color:

VI_Color
the (V-I) color index in Cousins' photometric system it represents the best available (V-I) value at the time of the Hipparcos Catalog publication.

VI_Color_Error
The standard error in the (V-I) color index, VI_Color.

VI_Color_Source
The Source of the (V-I) color index, VI_Color (see Section 1.3, Appendix 5 of the published Hipparcos Catalog for full details):

Mag_Ref_Dbl
A reference flag for the (B-V) and (V-I) color indices and the V magnitude Vmag (and all their standard errors) which is set to '*' when they refer to the combined light of double or multiple systems which are otherwise resolved by the main mission astrometry and photometry.

HIP_Mag
The median magnitude H_P in the Hipparcos photometric system, and defined on the basis of the accepted observations (or field transits) for a given star. Note that the Hipparcos magnitude could not be determined for 14 stars.

HIP_Mag_Error
The standard error of the median magnitude H_P.

Scat_HIP_Mag
The scatter of the H_P observations.

N_Obs_HIP_Mag
The number of H_P observations: this is the number of photometric observations (or field transits) used for the construction of the median, standard error, and scatter in H_P.

HIP_Mag_Ref_Dbl
A reference flag for the Hipparcos photometric parameters. For a double or multiple entry, this flag indicates that the photometry refers to:

HIP_Mag_Max
The observed magnitude at maximum luminosity. This is defined as the 5th percentile of the epoch photometry.

HIP_Mag_Min
The observed magnitude at minimum luminosity. This is defined as the 95th percentile of the epoch photometry.

Var_Period
The variability period, or a provisional estimate of such a period, derived on the basis of the Hipparcos data (possibly in combination with ground-based observations) and expressed in days, with a precision of 0.01 days.

HIP_Var_Type
The variability type: the sources of scatter in the photometric data are various, and this flag indicates the origin of the extra scatter, which may be astrophysical, or, in some cases, instrumental. See Section 1.3, Appendix 2 of the published Hipparcos Catalog for a more detailed description. Amongst astrophysical sources of variability, this parameter only distinguishes between 'M' (micro-variables), 'P' (periodic variables), and 'U' (unsolved variables). Further variability details for the periodic or unsolved variables are included in the Variability Annex. The flag takes the following values:

Var_Data_Annex
A Variability Annex flag indicating the existence of additional tabular data in the Variability Annex, where Ƈ' means that additional data are provided in a table of periodic variables, and ƈ' means that additional data are provided in a table of 'unsolved' variables.

Var_Curv_Annex
A Variability Annex flag indicating the existence of a light curve, or a folded light curve, in the Variability Annex, where 'A' means the light curve is folded, and 'B' or 'C' mean that the light curve is NOT folded.

CCDM_ID
The Catalog of Components of Double and Multiple Stars (CCDM) identifier.

CCDM_History
The historical status of the CCDM identifier. The flag takes the following values:

CCDM_N_Entries
The number of separate catalog entries with the same CCDM identifier.

CCDM_N_Comp
The number of components into which the entry was resolved as a result of the satellite observations and data reductions.

Dbl_Mult_Annex
The Double and Multiple Systems Annex flag. This indicates that further details of this system are given in one of the 5 (mutually exclusive) parts of the Double and Multiple Systems Annex labelled as follows:

Astrom_Mult_Source
A flag for the source of the absolute astrometry. This parameter qualifies the source of the astrometric parameters for some of the entries with a value of 'C' for the parameter Dbl_Mult_Annex. The values are as follows:

Dbl_Soln_Qual
A solution quality flag which indicates the reliability of the double or multiple star solution, and is set for all entries in Part C of the Double and Multiple Systems Annex. The flags can be understood as follows:

Dbl_Ref_ID
Component designation for the double star parameters, Dbl_theta, dbl_rho, etc. The first letter gives the 'reference' component, and the second letter gives the subsidiary component. In the case of the Hipparcos observations, the reference component is always defined to be the brighter component (in median H_P) such that the magnitude difference between the components (Diff_Hip_Mag) is always positive.

Dbl_Theta
The rounded value for the position angle between the components specified in the Dbl_Ref_id field, expressed in degrees (in the usual sense measured counterclockwise from North).

Dbl_Rho
The rounded value for the angular separation between the components specified in the Dbl_Ref_id field, expressed in arcseconds.

Rho_Error
The standard error of the angular separation, Dbl_Rho, given in arcseconds.

Diff_HIP_Mag
The Hipparcos magnitude difference of the components specified in the Dbl_Ref_id field, expressed in magnitudes.

Dhip_Mag_Error
The standard error of the Hipparcos magnitude difference, expressed in magnitudes.

Survey_Star
A flag indicating a survey' star. The survey' was the basic list of bright stars added to and merged with the total list of proposed stars, to provide a stellar sample (almost) complete to well-defined limits. A flag 'S' indicates that the entry is contained within this survey', whose limiting magnitude is a function of the stars's spectral type and galactic latitude b and is defined by: If no spectral data were available, the break was taken at (B-V) = 0.8 mag.

ID_Chart
A flag indicating an identification chart. Where identification of a star using ground-based telescopes might prove difficult or ambiguous, identification chrats were constructed and are available in Volume 13 of the printed catalog. Charts correspond to the object observed by the satellite (i.e., at the posotion given in this catalog), even if it was not the intended target. The flag takes the following values: 'D' for charts produced directly from the STScI Digitized Sky Survey (776 entries) or 'G' for charts constructed from the Guide Star Catalog (10877 entries).

Notes
A flag indicating a note is given at the end of the volume(s) in the printed catalog. The flag has the following meaning:

HD_ID
HD/HDE/HDEC identifier (CDS Catalog <III 135>).

BD_ID
Bonner Durchmusterung (BD) identifier (CDS Catalogs <I 119>, <I 122>). BD identifiers, unlike the CoD and CPD identifiers, may carry a suffix letter for additional stars, i.e., stars with suffixes 'A', "B', 'P', or 'S': these stars were added to the BD Catalog after the original numbering was made, and such suffixes do not imply that the entry is a component of a double or multiple system.

CoD_ID
Cordoba Durchmusterung (CoD) identifier (CDS Catalog <I 114>).

CPD_ID
Cape Photographic Durchmusterung (CPD) identifier (CDS Catalog <I 108>).

VI_Color_Reduct
The (V-I) color index used for the photometric processing (not necessarily the same as the final' value given in the parameter VI_mag).

Spect_Type
The MK or HD spectral type acquired from ground-based compilations and primarily taken from the Hipparcos Input Catalog, with some updates, especially for variable stars.

Spect_Type_Source
The source of the spectral type. The flag indicates the source as follows:

Class
The Browse classification created by the HEASARC based on the value of the spect_type parameter.