2.1 cepheid

This table describes the Cepheid stars identified in table variable_summary as classification="CEP". In the analyses only observations with
rejected_by_variability_processing=false are included, as found in table phot_variable_time_series_gfov.

Columns description:

type_best_classification : Best type classification estimate out of: ”DCEP”, ”T2CEP”, ”ACEP” (string, Dimensionless[see description])

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, Dimensionless[see description])

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”,”UNDEFINED”,”NOT_APPLICABLE” (string, Dimensionless[see description])

Best mode classification estimate:

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  ”FUNDAMENTAL”: fundamental mode for type_best_classification="DCEP" or "ACEP"

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  ”FIRST_OVERTONE”: first overtone for type_best_classification="DCEP" or "ACEP"

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  ”SECOND_OVERTONE”: second overtone for type_best_classification="DCEP" or "ACEP"

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  ”UNDEFINED”: if mode could not be clearly determined for type_best_classification="DCEP" or "ACEP"

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  ”NOT_APPLICABLE”: when type_best_classification="T2CEP"

Cepheid pulsation mode is assigned using the period-luminosity relations, which are different for the various pulsation modes, and the plot of the Fourier parameter R21 vs Period.

solution_id : Solution Identifier (long)

The data in the MDB will be described by means of a ”Solution identifier” parameter. This will be a numeric field attached to each table row that can be used to unequivocally identify the version of all the subsystems that where used in the generation of the data as well as the input data used. Each DPC generating the data will have the freedom to choose the Solution identifier number, but they must ensure that given the Solution identifier they can provide detailed information about the ”conditions” used to generate the data: versions of the software, version of the data used…

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)

p1 : Period corresponding to the maximum power peak in the periodogram of G band time series (double, Time[day])

This parameter is filled with the period of the maximum power peak in the frequencygram obtained from the modeling of the time series. The light curve of the target star is modeled with a truncated Fourier series ($mag(t_j)=zp+\sum [A_{i}sin(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$). Zero-point (zp), period (1/${\nu }_{max}$), number of harmonics ($i$), amplitudes ($A_i$), and phases (${\varphi }_i$) of the harmonics, for the G-band light curve are determined using the Levenberg-Marquardt non linear fitting algorithm.

p1_error : Uncertainty on the p1 period (double, Time[day])

This parameter is filled with the uncertainty value of the p1 parameter. Its value is derived with Monte Carlo simulations that generate several (100) time series with the same time path as the data points but with magnitudes generated randomly around the corresponding data value. For each of these time series the period is derived from the non linear modeling with a truncated Fourier series of the light curve. The mean of all the periods found and its standard deviation are then computed, and the latter value is kept as value to fill the p1_error parameter.

epoch_g : Epoch of the maximum of the light curve in the G band (double, Time[Barycentric JD in TCB - 2455197.5 (day)])

The epoch of maximum light for the Gaia integrated $G$ band. It corresponds to the Baricentric Julian day (BJD) of the maximum value of the light curve model which is closest to the BJD of the first observations -3$\times$p1.

The mentioned BJD is offset by JD 2455197.5 (= J2010.0).

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

The uncertainty value of the epoch_g parameter. Its value is three times the error on the p1.

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

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 (double, Magnitude[mag])

This parameter is filled with the uncertainty value of the int_average_g parameter. The uncertainty is computed as the $error(zp)$, where $zp$ is the zero point obtained by the non linear Fourier modeling of the light curve.

peak_to_peak_g : Peak-to-peak amplitude of the G band light curve (double, 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 folded modeled light curve in the $G$ band. The light curve of the target star is modeled with a truncated Fourier series ($mag(t_j)=zp+\sum [A_{i}sin(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$). Zero-point (zp), period (1/${\nu }_{max}$), number of harmonics ($i$), amplitudes ($A_i$), and phases (${\varphi }_i$) of the harmonics, for the $G$-band light curve are determined using the Levenberg-Marquardt non linear fitting algorithm.

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

This parameter is filled with the uncertainty value of the peak_to_peak_g parameter. The uncertainty is computed as the $\sqrt{2}\times error(zp)$, where $zp$ is the zero point obtained by the non linear Fourier modeling of the light curve.

num_harmonics_for_p1 : Number of harmonics used to model P1 of the light curve (int, Dimensionless[see description])

This parameter is filled with the number of harmonics used to model P1 of the light curve. The light curve of the target star is modeled with a truncated Fourier series ($mag(t_j)=zp+\sum [A_{i}sin(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$). 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 : Fourier decomposition parameter r21_g: A2/A1 (for G band) (double, Dimensionless[see description])

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 hereafter. The light curve of the target star is modeled with a truncated Fourier series ($mag(t_j)=zp+\sum [A_{i}sin(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$). 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) (double, Dimensionless[see description])

This parameter is filled with the uncertainty value on the r21_g parameter. Its value isderived by propagation of the errors in the A2 and A1 parameters. Errors in A1,A2 are computed from Monte Carlo simulations that generate several (100) time series with the same time path as the data points but with magnitudes generated randomly around the corresponding data value. The mean for each of these values and their standard deviations are then computed, and the latter values are kept as value to fill the uncertainty of the A1, A2 parameters.

phi21_g : Fourier decomposition parameter phi21_g: phi2 - 2*phi1 (for G band) (double, Dimensionless[see description])

This parameter is filled with the Fourier decomposition parameter ${\varphi }_{21}$: ${\varphi }_2-2{\varphi }_1$ value. The light curve of the target star is modeled with a truncated Fourier series ($mag(t_j)=zp+\sum [A_{i}sin(i\times 2\pi {\nu }_{max}{t}_j+{\varphi }_i)]$). Zero-point ($zp$), period (1/${\nu }_{max}$), number of harmonics ($i$), amplitudes ($A_i$), and phases (${\varphi }_i$) of the harmonics, for the $G$-band light curve 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) (double, Dimensionless[see description])

This parameter is filled with the uncertainty of the phi21_g parameter. Its value is derived by propagation of the errors in the phi1 and phi2 parameters. Errors in phi1,phi2 are computed from Monte Carlo simulations that generate several (100) time series with the same time path as the data points but with magnitudes generated randomly around the corresponding data value. For each of these time series the phi1, phi2 values are computed. The mean for each of these values and their standard deviation are then computed, and the latter values are kept as value to fill the uncertainty of the phi1 and phi2 parameters.