20.13.6 vari_cepheid

This table describes the Cepheid stars.

Columns description:

solution_id : Solution Identifier (long)

All Gaia data processed by the Data Processing and Analysis Consortium comes tagged with a solution identifier. This is a numeric field attached to each table row that can be used to unequivocally identify the version of all the subsystems that were used in the generation of the data as well as the input data used. It is mainly for internal DPAC use but is included in the published data releases to enable end users to examine the provenance of processed data products. To decode a given solution ID visit https://gaia.esac.esa.int/decoder/solnDecoder.jsp

source_id : Unique source identifier (long)

A unique single numerical identifier of the source obtained from gaia_source (for a detailed description see gaia_source.source_id).

pf : Period corresponding to the fundamental pulsation mode in the G band time series (double, Time[day])

For single-mode pulsators classified as fundamental mode pulsators, this parameter is filled with the periodicity found in the time-series.

This value is obtained by modelling the $G$ band time series using the Levenberg-Marquardt non–linear fitting algorithm (Clementini et al. 2016).

Information for vari_rrlyrae: For double-mode RR Lyrae this parameter is filled with the period corresponding to the longer periodicity.

Information for vari_cepheid: For double-mode DCEPs this parameter is filled with the period corresponding to the longer periodicity if the DCEP is classified as ‘F/1O’ or ‘F/2O’. For triple-mode DCEPs this parameter is filled with the period corresponding to the longer periodicity if the DCEP is classified as ‘F/1O/2O’.

pf_error : Uncertainty of the pf period (float, Time[day])

This parameter is filled with the uncertainty of the pf parameter, computed via a bootstrap technique.

p1_o : Period corresponding to the first overtone pulsation mode in the G band time series (double, Time[day])

For single-mode pulsators classified as first-overtone pulsators, this parameter is filled with the periodicity found in the time-series.

This value is obtained by modelling the $G$ time series using the Levenberg-Marquardt non linear fitting algorithm (see Clementini et al. 2016).

Information for vari_rrlyrae: For double-mode RR Lyrae this parameter is filled with the period corresponding to the shortest periodicity.

Information for vari_cepheid: For double-mode DCEPs this parameter is filled with the period corresponding to the shortest periodicity if the DCEP is classified as ‘F/1O’; otherwise it is filled with the longest one if the classification is ‘1O/2O’ or ‘1O/3O’. For triple-mode DCEPs this parameter is filled with the period corresponding to the intermediate periodicity if the DCEP is classified as ‘F/1O/2O’; it is filled with the longest periodicity if the classification is ‘1O/2O/3O’.

p1_o_error : Uncertainty of the p1_o period (float, Time[day])

This parameter is filled with the uncertainty of the p1_o parameter, computed via a bootstrap technique.

epoch_g : Epoch of the maximum of the light curve in the G band (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Epoch of maximum light for the Gaia $G$ band light curve. It corresponds to the barycentric Julian day (BJD) of the maximum value of the light curve model which is closest to the BJD of the first observations -3 times the period of the source (first periodicity depending on the pulsation mode).

The aforementioned BJD is offset by JD 2 455 197.5 (= J2010.0).

epoch_g_error : Uncertainty on the epoch parameter epoch_g (float, Time[day])

Value of the uncertainty of the epoch_g parameter. It corresponds to three times the error on the period of the source (first periodicity depending on the pulsation mode).

epoch_bp : Epoch of the maximum of the light curve in the BP band (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Epoch of maximum light for the Gaia integrated $G_{\mathrm{BP}}$ band light curve. It corresponds to the barycentric Julian day (BJD) of the maximum value of the light curve model which is closest to the BJD of the first observations -3 times the period of the source (first periodicity depending on the pulsation mode).

The aforementioned BJD is offset by JD 2 455 197.5 (= J2010.0).

epoch_bp_error : Uncertainty on the epoch parameter epoch_bp (float, Time[day])

Value of the uncertainty of the epoch_bp parameter. It corresponds to three times the error on the period of the source (first periodicity depending on the pulsation mode).

epoch_rp : Epoch of the maximum of the light curve in the RP band (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Epoch of maximum light for the Gaia integrated $G_{\mathrm{RP}}$ band light curve. It corresponds to the barycentric Julian day (BJD) of the maximum value of the light curve model which is closest to the BJD of the first observations -3 times the period of the source (first periodicity depending on the pulsation mode).

The aforementioned BJD is offset by JD 2 455 197.5 (= J2010.0).

epoch_rp_error : Uncertainty on the epoch parameter epoch_rp (float, Time[day])

Value of the uncertainty of the epoch_rp parameter. It corresponds to three times the error on the period of the source (first periodicity depending on the pulsation mode).

epoch_rv : Epoch of the minimum of the radial velocity curve (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Epoch of minimum radial velocity for the Gaia radial velocity curve.

epoch_rv_error : Uncertainty on the epoch parameter epoch_rv (float, Time[day])

Value of the uncertainty of the epoch_rv parameter. It corresponds to three times the error on the period of the source (first periodicity depending on the pulsation mode).

int_average_g : Intensity-averaged magnitude in the G band (float, Magnitude[mag])

Value of the intensity-averaged magnitude in the $G$-band. The intensity-averaged magnitude is obtained by computing the average flux and then converting the average flux to magnitude.

int_average_g_error : Uncertainty on int_average_g parameter (float, Magnitude[mag])

This parameter is filled with the uncertainty of the int_average_g parameter, computed via a bootstrap technique.

int_average_bp : Intensity-averaged magnitude in the BP band (float, Magnitude[mag])

Value of the intensity-averaged magnitude in the $G_{\mathrm{BP}}$-band. The intensity-averaged magnitude is obtained by computing the average flux and then converting the average flux to magnitude.

int_average_bp_error : Uncertainty on int_average_bp parameter (float, Magnitude[mag])

This parameter is filled with the uncertainty of the int_average_bp parameter, computed via a bootstrap technique.

int_average_rp : Intensity-averaged magnitude in the RP band (float, Magnitude[mag])

Value of the intensity-averaged magnitude in the $G_{\mathrm{RP}}$-band. The intensity-averaged magnitude is obtained by computing the average flux and then converting the average flux to magnitude.

int_average_rp_error : Uncertainty on int_average_rp parameter (float, Magnitude[mag])

This parameter is filled with the uncertainty of the int_average_rp parameter, computed via a bootstrap technique.

average_rv : Mean radial velocity (float, Velocity[km s${}^{-1}$])

Average value of the Fourier modelled radial velocity curve, provided by the $A_0$ parameter of the Fourier fit.

average_rv_error : Uncertainty on average_rv parameter (float, Velocity[km s${}^{-1}$])

Error of average_rv computed via bootstrap technique.

peak_to_peak_g : Peak-to-peak amplitude of the G band light curve (float, Magnitude[mag])

This parameter is filled with the peak-to-peak amplitude value of the $G$ band light curve. The peak-to-peak amplitude is calculated as the (maximum) - (minimum) of the modelled folded light curve in the $G$ band. The light curve of the target star is modelled with a truncated Fourier series.

peak_to_peak_g_error : Uncertainty on the peak_to_peak_g parameter (float, Magnitude[mag])

This parameter is filled with the uncertainty value of the peak_to_peak_g parameter, computed via a bootstrap technique.

peak_to_peak_bp : Peak-to-peak amplitude of the BP band light curve (float, Magnitude[mag])

This parameter is filled with the peak-to-peak amplitude value of the $G_{\mathrm{BP}}$ light curve. The peak-to-peak amplitude is calculated as the (maximum) - (minimum) of the modelled folded light curve in the $G_{\mathrm{BP}}$ band. The light curve of the target star is modelled with a truncated Fourier series.

peak_to_peak_bp_error : Uncertainty on the peak_to_peak_bp parameter (float, Magnitude[mag])

This parameter is filled with the uncertainty value of the peak_to_peak_bp parameter, computed via a bootstrap technique.

peak_to_peak_rp : Peak-to-peak amplitude of the RP band light curve (float, Magnitude[mag])

This parameter is filled with the peak-to-peak amplitude value of the $G_{\mathrm{RP}}$ light curve. The peak-to-peak amplitude is calculated as the (maximum) - (minimum) of the modelled folded light curve in the $G_{\mathrm{RP}}$ band. The light curve of the target star is modelled with a truncated Fourier series.

peak_to_peak_rp_error : Uncertainty on the peak_to_peak_rp parameter (float, Magnitude[mag])

This parameter is filled with the uncertainty value of the peak_to_peak_rp parameter, computed via a bootstrap technique.

peak_to_peak_rv : Peak-to-peak amplitude of the radial velocity curve (double, Velocity[km s${}^{-1}$])

This parameter is filled with the peak-to-peak amplitude value of the radial velocity curve. The peak-to-peak amplitude is calculated as the (maximum) - (minimum) of the modelled folded $RV$ curve. The $RV$ curve of the target star is modelled with a truncated Fourier series.

peak_to_peak_rv_error : Uncertainty on the peak_to_peak_rv parameter (double, Velocity[km s${}^{-1}$])

This parameter is filled with the uncertainty value of the peak_to_peak_rv parameter, computed via a bootstrap technique.

metallicity : Metallicity of the star from the Fourier parameters of the light curve (float, Abundances[dex])

This parameter is filled with the [Fe/H] metallicity derived for the source from the Fourier parameters of the $G$-band light curve.

metallicity_error : Uncertainty of the metallicity parameter (float, Abundances[dex])

This parameter is filled with the uncertainty of the metallicity derived from the Fourier parameters of the $G$-band light curve.

r21_g : Fourier decomposition parameter r21_g: A2/A1 (for G band) (float)

This parameter is filled with the Fourier decomposition parameter $R_{21}=A_2/A_1$, where $A_2$ is the amplitude of the 2nd harmonic and $A_1$ is the amplitude of the fundamental harmonic of the truncated Fourier series defined as ($mag(t_j)=zp+\sum [A_{i}cos(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$) used to model the $G$-band light curve. Zero-point ($zp$), period (1/${\nu }_{max}$), number of harmonics ($i$), amplitudes ($A_i$), and phases (${\varphi }_i$) of the harmonics, are determined using the Levenberg-Marquardt non linear fitting algorithm.

r21_g_error : Uncertainty on the r21_g parameter: A2/A1 (for G band) (float)

This parameter is filled with the uncertainty value on the r21_g parameter, computed via a bootstrap technique.

r31_g : Fourier decomposition parameter r31_g: A3/A1 (for G band) (float)

This parameter is filled with the Fourier decomposition parameter $R_{21}=A_3/A_1$, where $A_3$ is the amplitude of the 3rd harmonic and $A_1$ is the amplitude of the fundamental harmonic of the truncated Fourier series defined as ($mag(t_j)=zp+\sum [A_{i}cos(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$) used to model the $G$-band light curve. Zero-point ($zp$), period (1/${\nu }_{max}$), number of harmonics ($i$), amplitudes ($A_i$), and phases (${\varphi }_i$) of the harmonics, are determined using the Levenberg-Marquardt non linear fitting algorithm.

r31_g_error : Uncertainty on the r31_g parameter: A3/A1 (for G band) (float)

This parameter is filled with the uncertainty value of the r31_g parameter, computed via a bootstrap technique.

phi21_g : Fourier decomposition parameter phi21_g: phi2 - 2*phi1 (for G band) (float, Angle[rad])

This parameter is filled with the Fourier decomposition parameter ${\varphi }_{21}$: ${\varphi }_2-2{\varphi }_1$ value, where ${\varphi }_2$ is the phase of the 2nd harmonic and ${\varphi }_1$ is the phase of the fundamental harmonic of the truncated Fourier series defined as ($mag(t_j)=zp+\sum [A_{i}cos(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$) used to model the $G$-band light curve. Zero-point ($zp$), period (1/${\nu }_{max}$), number of harmonics ($i$), amplitudes ($A_i$), and phases (${\varphi }_i$) of the harmonics, are determined using the Levenberg-Marquardt non linear fitting algorithm.

phi21_g_error : Uncertainty on the phi21_g parameter: phi2 - 2*phi1 (for G band) (float, Angle[rad])

This parameter is filled with the uncertainty of the phi21_g parameter, computed via a bootstrap technique.

phi31_g : Fourier decomposition parameter phi31_g: phi3 - 3*phi1 (for G band) (float, Angle[rad])

This parameter is filled with the Fourier decomposition parameter ${\varphi }_{31}$: ${\varphi }_3-3{\varphi }_1$ value, where ${\varphi }_3$ is the phase of the 3rd harmonic and ${\varphi }_1$ is the phase of the fundamental harmonic of the truncated Fourier series defined as ($mag(t_j)=zp+\sum [A_{i}cos(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$) used to model the $G$-band light curve. Zero-point ($zp$), period (1/${\nu }_{max}$), number of harmonics ($i$), amplitudes ($A_i$), and phases (${\varphi }_i$) of the harmonics, are determined using the Levenberg-Marquardt non linear fitting algorithm.

phi31_g_error : Uncertainty on the phi31_g parameter: phi3 - 3*phi1 (for G band) (float, Angle[rad])

This parameter is filled with the uncertainty of the phi31_g: ${\varphi }_3-3{\varphi }_1$ parameter, computed via a bootstrap technique.

num_clean_epochs_g : Number of G FoV epochs used in the fitting algorithm (short)

This parameter is filled with the number of epochs that remain in the $G$-band light curve after the SOS Cep & RRLyrae outlier removal process.

num_clean_epochs_bp : Number of BP epochs used in the fitting algorithm (short)

This parameter is filled with the number of epochs that remain in the $G_{\mathrm{BP}}$-band light curve after the SOS Cep & RRLyrae outlier removal process.

num_clean_epochs_rp : Number of RP epochs used in the fitting algorithm (short)

This parameter is filled with the number of epochs that remain in the $G_{\mathrm{RP}}$-band light curve after the SOS Cep & RRLyrae outlier removal process.

num_clean_epochs_rv : Number of radial velocity epochs used in the fitting algorithm (short)

This parameter is filled with the number of epochs that remain in the radial velocity curve after the SOS Cep & RRLyrae outlier removal process.

zp_mag_g : Zero point (mag) of the final model of the G band light curve (float, Magnitude[mag])

Zero point (mag) of the final model of the $G$-band light curve for Cepheids and RR Lyrae stars.

zp_mag_bp : Zero point (mag) of the final model of the BP band light curve (float, Magnitude[mag])

Zero point (mag) of the final model of the $G_{BP}$ band light curve for Cepheids and RR Lyrae stars.

zp_mag_rp : Zero point (mag) of the final model of the RP band light curve (float, Magnitude[mag])

Zero point (mag) of the final model of the $G_{RP}$ band light curve for Cepheids and RR Lyrae stars.

num_harmonics_for_p1_g : Number of harmonics used to model the first periodicity of the G-band light curve (byte)

This parameter is filled with the number of harmonics used to model the $G$-band light curve folded with the P1 period. The $G$-band light curve of the target star is modelled with a truncated Fourier series.

num_harmonics_for_p1_bp : Number of harmonics used to model the first periodicity of the BP-band light curve (byte)

This parameter is filled with the number of harmonics used to model the $G_{\mathrm{BP}}$-band light curve folded with the P1 period. The $G_{\mathrm{BP}}$-band light curve of the target star is modelled with a truncated Fourier series.

num_harmonics_for_p1_rp : Number of harmonics used to model the first periodicity of the RP-band light curve (byte)

This parameter is filled with the number of harmonics used to model the $G_{\mathrm{RP}}$-band light curve folded with the P1 period. The $G_{\mathrm{RP}}$-band light curve of the target star is modelled with a truncated Fourier series.

num_harmonics_for_p1_rv : Number of harmonics used to model the first periodicity of the radial velocity curve (byte)

This parameter is filled with the number of harmonics used to model the radial velocity curve folded with the P1 period. The radial velocity curve of the target star is modelled with a truncated Fourier series.

reference_time_g : Reference time of the Fourier modelled G-band light curve (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Reference time for the Fourier modelled $G$-band light curve.

reference_time_bp : Reference time of the Fourier modelled BP-band light curve (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Reference time for the Fourier modelled $G_{\mathrm{BP}}$-band light curve.

reference_time_rp : Reference time of the Fourier modelled RP-band light curve (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Reference time for the Fourier modelled $G_{\mathrm{RP}}$-band light curve.

reference_time_rv : Reference time of the Fourier modelled radial velocity curve (double, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Reference time for the Fourier modelled radial velocity curve.

fund_freq1 : First frequency of the non-linear Fourier modelling (double, Frequency[day${}^{-1}$])

First frequency of the non-linear Fourier modelling. It applies to all three $G$, $G_{\mathrm{BP}}$, and $G_{\mathrm{RP}}$ bands and the radial velocity curve.

fund_freq1_error : Error of the first frequency of the non-linear Fourier modelling (float, Frequency[day${}^{-1}$])

Error of the first frequency of the non-linear Fourier modelling.

fund_freq2 : Second frequency of the non-linear Fourier modelling in the G band (double, Frequency[day${}^{-1}$])

Second frequency of the non-linear Fourier modelling for the $G$ band only.

fund_freq2_error : Error of the second frequency of the non-linear Fourier modelling in the G band (float, Frequency[day${}^{-1}$])

Error of the second frequency of the non-linear Fourier modelling. It applies to the $G$ band only.

fund_freq1_harmonic_ampl_g : Amplitudes of the Fourier model for the first frequency in the G band (float[16] array, Magnitude[mag])

Amplitudes of the Fourier model fitted to the observed $G$-band light curve.

fund_freq1_harmonic_ampl_g_error : Errors of the amplitudes of the Fourier model for the first frequency in the G band (float[16] array, Magnitude[mag])

Errors of the amplitudes of the Fourier model fitted to the observed $G$-band light curve.

fund_freq1_harmonic_phase_g : Phases of the Fourier model for the first frequency in the G band (float[16] array, Angle[rad])

Phases of the Fourier model fitted to the observed $G$-band light curve.

fund_freq1_harmonic_phase_g_error : Errors of the phases of the Fourier model for the first frequency in the G band (float[16] array, Angle[rad])

Errors of the phases of the Fourier model fitted to the observed $G$-band light curve.

fund_freq1_harmonic_ampl_bp : Amplitudes of the Fourier model for the first frequency in the BP band (float[16] array, Magnitude[mag])

Amplitudes of the Fourier model fitted to the observed $G_{\mathrm{BP}}$-band light curve.

fund_freq1_harmonic_ampl_bp_error : Errors of the amplitudes of the Fourier model for the first frequency in the BP band (float[16] array, Magnitude[mag])

Errors of the amplitudes of the Fourier model fitted to the observed $G_{\mathrm{BP}}$-band light curve.

fund_freq1_harmonic_phase_bp : Phases of the Fourier model for the first frequency in the BP band (float[16] array, Angle[rad])

Phases of the Fourier model fitted to the observed $G_{\mathrm{BP}}$-band light curve.

fund_freq1_harmonic_phase_bp_error : Errors of the phases of the Fourier model for the first frequency in the BP band (float[16] array, Angle[rad])

Errors of the phases of the Fourier model fitted to the observed $G_{\mathrm{BP}}$-band light curve.

fund_freq1_harmonic_ampl_rp : Amplitudes of the Fourier model for the first frequency in the RP band (float[16] array, Magnitude[mag])

Amplitudes of the Fourier model fitted to the observed $G_{\mathrm{RP}}$-band light curve.

fund_freq1_harmonic_ampl_rp_error : Errors of the amplitudes of the Fourier model for the first frequency in the RP band (float[16] array, Magnitude[mag])

Errors of the amplitudes of the Fourier model fitted to the observed $G_{\mathrm{RP}}$-band light curve.

fund_freq1_harmonic_phase_rp : Phases of the Fourier model for the first frequency in the RP band (float[16] array, Angle[rad])

Phases of the Fourier model fitted to the observed $G_{\mathrm{RP}}$-band light curve.

fund_freq1_harmonic_phase_rp_error : Errors of the phases of the Fourier model for the first frequency in the RP band (float[16] array, Angle[rad])

Errors of the phases of the Fourier model fitted to the observed $G_{\mathrm{RP}}$-band light curve.

fund_freq1_harmonic_ampl_rv : Amplitudes of the Fourier model for the first frequency of the radial velocity curve (float[16] array, Velocity[km s${}^{-1}$])

Amplitudes of the Fourier model fitted to the observed radial velocity curve.

fund_freq1_harmonic_ampl_rv_error : Errors of the amplitudes of the Fourier model for the first frequency of the radial velocity curve (float[16] array, Velocity[km s${}^{-1}$])

Errors of the amplitudes of the Fourier model fitted to the observed radial velocity curve.

fund_freq1_harmonic_phase_rv : Phases of the Fourier model for the first frequency of the radial velocity curve (float[16] array, Angle[rad])

Phases of the Fourier model fitted to the observed radial velocity curve.

fund_freq1_harmonic_phase_rv_error : Errors of the phases of the Fourier model for the first frequency of the radial velocity curve (float[16] array, Angle[rad])

Errors of the phases of the Fourier model fitted to the observed radial velocity curve.

p2_o : Period corresponding to the second overtone pulsation mode (for multi mode pulsators) in the G band time series (double, Time[day])

For double-mode DCEPs, this parameter is filled with the period corresponding to the shortest periodicity if the DCEP is classified as ‘1O/2O’ of ‘F/2O’; otherwise it is filled with the longest periodicity if the classification is ‘2O/3O’.

For triple-mode DCEPs this parameter is filled with the period corresponding to the shortest periodicity if the DCEP is classified as ‘F/1O/2O’; it is filled with the intermediate periodicity if the classification is ‘1O/2O/3O’.

This value is obtained by modelling the $G$ time series using the Levenberg-Marquardt non linear fitting algorithm (see Clementini et al. 2016).

p2_o_error : Uncertainty of the p2_o period (float, Time[day])

This parameter is filled with the uncertainty of the p2_o parameter, computed via a bootstrap technique.

type_best_classification : Best type classification estimate out of: ‘DCEP’, ‘T2CEP’, ‘ACEP’ (string)

Classification of a Cepheid into ‘DCEP’, ‘T2CEP’ or ‘ACEP’ using the period-luminosity relations, which are different for the three different types of Cepheids.

type2_best_sub_classification : Best subclassification estimate for type_best_classification=‘T2CEP’ out of: ‘BL_HER’, ‘W_VIR’,‘RV_TAU’ (string)

Sub-classification of a T2CEP Cepheids into BL Herculis (‘BL_HER’), W Virginis (‘W_VIR’) or RV Tauris (‘RV_TAU’) sub-types depending on the source periodicity.

mode_best_classification : Best mode classification estimate out of: ‘FUNDAMENTAL’, ‘FIRST_OVERTONE’, ‘SECOND_OVERTONE’, ‘MULTI’,‘UNDEFINED’, ‘NOT_APPLICABLE’ (string)

Best mode classification estimate:

• •

  ‘FUNDAMENTAL’: fundamental mode for type_best_classification=‘DCEP’ or ‘ACEP’

• •

  ‘FIRST_OVERTONE’: first overtone for type_best_classification=‘DCEP’ or ‘ACEP’

• •

  ‘SECOND_OVERTONE’: second overtone for type_best_classification=‘DCEP’

• •

  ‘MULTI’: multi-mode pulsators for type_best_classification=‘DCEP’

• •

  ‘UNDEFINED’: if mode could not be clearly determined for type_best_classification=‘DCEP’ or ‘ACEP’

• •

  ‘NOT_APPLICABLE’: when type_best_classification=‘T2CEP’

The Cepheid pulsation mode is assigned using the period-luminosity and period-Wesenheit relations, which are different for the various pulsation modes as well as analysing the Fourier parameters vs period plots. The type ‘MULTI’ is assigned to stars pulsating in two or more modes simultaneously.

multi_mode_best_classification : Best multi mode DCEP classification out of: ‘F/1O’, ‘F/2O’, ‘1O/2O’, ‘1O/3O’, ‘2O/3O’, ‘F/1O/2O’, ‘1O/2O/3O’ (string)

Sub-classification of multi mode DCEP variables according to their position in the ‘Petersen diagram’ — see for example Fig. 1 in Soszyński et al. (2015). F,1O,2O and 3O correspond with fundamental, first, second and third overtone, respectively.