VOSA. Help and Documentation

Version 6.0, Apr 2018

1. Introduction
2. Input files
2.1. Upload files
2.2. VOSA file format
2.3. Single object
2.4. Manage files
2.5. Archiving
2.6. Filters
3. Objects
3.1. Coordinates
3.2. Distances
3.3. Extinction
4. Build SEDs
4.1. VO photometry
4.2. SED
4.3. Excess
5. Analysis
5.1. Model Fit
5.2. Bayes analysis
5.3. Template Fit
5.4. Templates Bayes
5.5. HR diagram
5.6. Upper Limits
5.7. Statistics
6. Save results
6.1. Download
6.2. SAMP
6.3. References
6.4. Log file
6.5. Plots
7. VOSA Architecture
8. Phys. Constants
9. FAQ
10. Use Case
11. Quality
11.1. Stellar libraries
11.2. VO photometry
12. Credits
13. Helpdesk
14. About

Quality: Stellar libraries tests

Elodie library

To assess the performance of VOSA we have made a comparison with the Elodie library (v3.1).

For the comparison we have selected only those Elodie targets with a quality flag=4 ("excellent") in effective temperatures.

Then, for these targets, the observational SED has been built using photometry (Tycho, Stromgren and 2MASS) retrieved from VO services using VOSA.

An average value of Teff(VOSA)-Teff(Elodie)=-34 ± 150K is found for a sample of 116 objects.

Object Teff (fit) Teff (Elodie) Teff(fit)-Teff(Elodie)
BD+02337557505944-194
BD+02465160006046-46
BD+04455160005789211
BD+174708600059937
HD00069365006156344
HD00183557505777-27
HD00266550005004-4
HD0027965000492080
HD003567600059919
HD0043065000493367
HD00430757505806-56
HD0048136250618565
HD00501562506119131
HD0068334500443367
HD00956257505821-71
HD00982662506138112
HD01100757505975-225
HD01340355005653-153
HD0137835500545149
HD01767457505893-143
HD01947645004954-454
HD01999460006094-94
HD02248457505989-239
HD02931057505796-46
HD03056260005860140
HD03712455005602-102
HD03782845004343157
HD0388585750573020
HD0395876000591882
HD04358757505870-120
HD0439476000595545
HD04400747504881-131
HD045067600059982
HD04528252505273-23
HD04993365006515-15
HD05557557505895-145
HD0599846000590793
HD06160647504895-145
HD0637914750470347
HD06460650005182-182
HD0731084500443169
HD07615157505751-1
HD07693257505850-100
HD08180952505688-438
HD085503450044928
HD08714050005103-103
HD08860945004548-48
HD0887255750565892
HD08901055005667-167
HD0940286000598020
HD09512860005865135
HD10120645004601-101
HD10222445004343157
HD10497950004875125
HD1055465250522129
HD105755575057491
HD10721362506290-40
HD1080765750572327
HD10895460006043-43
HD11018442504336-86
HD11089757505890-140
HD11538362505979271
HD12256347504575175
HD12295645004617-117
HD12605355005661-161
HD12816765006782-282
HD13032252505410-160
HD13408365006589-89
HD13416957505831-81
HD13979865006798-298
HD14100460005890110
HD14428455006170-670
HD14457952505293-43
HD14623360005796204
HD15017760006064-64
HD1509975000492179
HD15708957505778-28
HD15922257505807-57
HD16109647504541209
HD16519542504450-200
HD16540157505816-66
HD16590855005957-457
HD16662050005013-13
HD16800957505793-43
HD17366765006329171
HD17491257505882-132
HD1844995750573317
HD18637957505863-113
HD18640857505787-37
HD18642757505757-7
HD18711140004298-298
HD18712357505804-54
HD18769162506137113
HD18851055005510-10
HD1895585750565595
HD1945986000598119
HD19563357505956-206
HD197076A57505798-48
HD19996057505848-98
HD20058057505818-68
HD20188955005614-114
HD20415557505753-3
HD20454345004680-180
HD20797862506289-39
HD2089066000597030
HD21294347504604146
HD21614345004511-11
HD2163856250621931
HD21701457505761-11
HD21710755005612-112
HD21885750005108-108
HD21962362506099151
HD2209544750468268
HD2218305750571931
HD2223686250616090
HD345957575057491

VOSA and hot stars.

To assess the performance of VOSA at high temperatures we have used the compilation of sdO stars made by Stroeer et al. (2007 A&A, 462, 269)

For our analysis we have selected only those sdO targets not flagged as "outliers" in effective temperature (Table1 of the paper). Then, for these targets, the observational SED has been built using photometry (GALEX, CMC-14, 2MASS) retrieved from VO services using VOSA. The following criteria were adopted:

  • J(2MASS) < 17
  • H(2MASS) < 16.2
  • K(2MASS)< 15
     
  • r (CMC-14) < 17
     
  • FUV (GALEX) > 12
  • NUV(GALEX)>11

An average value of Teff (VOSA)-Teff (Stroeer)=2800 ± 6700K is found for a sample of 14 objects.

Object Model Teff (fit) Teff (paper) Teff(fit)-Teff(paper)
HE0001-2443Husfeld50000.040975.09025.0
HE0111-1526Kurucz42000.039152.02848.0
HE0342-1702TLUSTY50000.041914.08086.0
HE0914-0314Husfeld50000.045136.04864.0
HE0958-1151Husfeld55000.044125.010875.0
HE1047-0637Husfeld65000.060650.04350.0
HE1136-1641TLUSTY45000.044646.0354.0
HE1203-1048TLUSTY40000.045439.0-5439.0
HE1238-1745Husfeld55000.038219.016781.0
HE1258+0113Husfeld37500.039359.0-1859.0
HE1310-2733Kurucz30000.040000.0-10000.0
HE1316-1834TLUSTY45000.042811.02189.0
HE1446-1058TLUSTY45000.045000.00.0
HE1513-0432TLUSTY40000.042699.0-2699.0

Comparison with Yee et al. (2017ApJ...836...77Y)

Date of this test: 2017/05/16

We compare the results in Yee et al. with the fit results obtained by VOSA.

  • Yee et al. (2017ApJ...836...77Y)
    • Library of optical spectra of 404 touchstone stars observed with Keck/HIRES. High-resolution (R~60000), high signal-to-noise (SNR~150/pixel).
    • Properties (M, R, Teff, [Fe/H]) derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry.
    • Spectral types ~ M5-F1 (Teff ~ 3000-7000K, Rstar ~ 0.1-1.6 Rsun).
  • SED building using VOSA
    • Photometric SED built using Galex, Gaia, APASS, 2MASS and WISE data.
    • Model fit using Kurucz (logg: 2.5 - 5.0; [M/H]: -1.5 - 0.5, Teff: 3500 - 10000 K)
    • Model fit using BT-Settl (logg: 2.5 - 6.0; [M/H]: -1.5 - 0.5, Teff: 3500 - 10000 K)

    Effective temperatures

    Only objects with good fit (vgfb<=12) and sigma<200K in the Bayesian fitting are considered (155 objects).

    Teff (Yee) - Teff(VOSA)

    • Mean: -4.91K
    • Std: 208.84K
    • Median: -34.77K

    Surface gravities

    Only objects with good fit (vgfb<=12) and sigma<0.3dex in the Bayesian fitting are considered (38 objects).

    logg (Yee) - logg (VOSA)

    • Mean: 1.14dex
    • Std: 0.64dex
    • Median: 1.24dex

    But if we use BT-Settl instead of Kurucz, the situation is the reverse, with the gravity values computed by VOSA systematically higher than those given in the paper (28 objects have been used this time).

    Metallicities

    Only objects with good fit (vgfb<=12) and sigma<0.3dex in the Bayesian fitting are considered (141 objects).

    [M/H] (Yee) - [M/H] (VOSA)

    • Mean: 0.16dex
    • Std: 0.58dex
    • Median: -0.02dex

    A similar result is obtained is BT-Settl is used:

    Radius

    Only objects with good fit (vgfb<=12) and errors in Parallaxes (TGAS) < 10% (190 objects).

    Excellent agreement between the distances used in the paper and those used in VOSA (from TGAS).

    Radius1 (VOSA); defined by: Md = (R/D)^2

    Radius1 (Yee) - Radius1 (VOSA)

    • Mean: -0.23 Rsun
    • Std: 0.47 Rsun
    • Median: -0.06 Rsun

    Radius2 (VOSA); defined by: Lbol = 4 * pi * R^2 * σ * Teff^4

    Radius2 (Yee) - Radius2 (VOSA)

    • Mean: -0.24 Rsun
    • Std: 0.50 Rsun
    • Median: -0.06 Rsun

    Similar plots are obtained if BT-Settl models are used instead.

    Masses

    Only objects with good fit (vgfb<=12). 54 objects (restricted to masses below 1.4 Msun)

    BTSettl isochrones and tracks.

    Excellent agreement for subsolar masses. Masses over 1Msun are overestimated in VOSA-BTSettl.

    Mass(Yee) - Mass (VOSA_BTSettl)

    • Mean: -0.11Msun
    • Std: 0.09Msun
    • Median: -0.13Msun

    Similar results are obtained if the BTSettl-CFITS isochrones and tracks are used:

    Comparison with Lindgren & Heiter 2017 (arXiv170508785L)

    Date of this test: 2017/07/18 (by Miriam Cortés Contreras)

    (Download this test in pdf)

    Summary

    We compare the results in Lindgren & Heiter 2017 (here-after LH17) with the fit results obtained with VOSA.

    • Effective temperatures

      Efective temperatures computed by VOSA are in agreement with those given in LH17. On average, LH17 temperatures are systematically higher by less than 100K both for BT-Settl and CIFITS. Standard deviations are below 150 K in both cases.

      Below 3400 K, LH17 effective temperatures are larger (250 K and 450 K) than those provided by BT-Settl. This trend does not appear if CIFITS models are used. Anyway, a larger number of objects would be neces- sary to confirm this result.

    • Surface gravities, metallicities

      As expected from the minor contribution of these parameters to the SED shape, the values obtained from VOSA are affected by large uncertainties and, thus, are not reliable.

    • Stellar radii

      There are not significant differences between the radii derived using BT-Settl or BT-Settl CIFIST models and both are in very good agreement with the values derived by LH17.

    • Stellar masses

      While masses directly derived from M = gR 2 /G are not reliable due to the large uncertainties associated to the surface gravities estimated with VOSA, those obtained using the BT-Settl and BHAC isochrones are in reasonable agreement with the ones obtained in LH17. The agreement is slightly worse if the BHAC isochrones are used.

    Sample and input parameters

    • Lindgren & Heiter 2017.
      • Parameter determination for sixteen cool dwarfs using high-resolution spectra taken with CRIRES at VLT:
        • J band (1100-1400 nm)
        • R = 50 000
        • SNR: 55-205
      • Stellar properties:
        • Temperatures determined from FeH lines for M dwarfs cooler than 3575 K, and from photometric calibration for warmer stars. 3350 < Teff[K] < 4550 (±100 K)
        • Metallicities determined using synthetic spectra fitting. -0.50 < [M/H] < +0.40 (±0.05 dex)
        • Spectral types: K4/K5 - M3.5 V
        • Masses derived from the mass-magnitude empirical relation by Benedict et al. (2016). 0.178 < M [M ] < 0.524
        • Radii derived from the mass-magnitude empirical relation by Mann et al. (2015). 0.214 < R [R ] < 0.698
        • Surface gravity (g = GM/R 2 ): 4.56 < log g [cm s-2 ] < 5.03
    • SED building using VOSA.
      • Photometric SED built using photometry from GALEX, Johnson, SDSS, TYCHO, APASS, GAIA, DENIS, 2MASS, WISE, AKARI and IRAS, retrieved from VO services.
      • Model fit using BT-Settl (log g : 4-6; [M/H]: -0.5-0.5, Teff: 3000 - 5500 K)
      • Model fit using BT-Settl CIFIST (log g : 4 - 6; [M/H] = 0, Teff: 3000 - 5500 K)

    Parameters determination

    For comparison and to assess whether the parameters obtained with VOSA are model-dependent, we performed this analysis using two models: BT-Settl and BT-Settl CIFIST. One of the sixteen stars has not enough photometric data. Thus, this analysis was carried out for the fifteen remaining stars.

    Effective Temperatures

    • BT-Settl (Fig. 1)

      Mean(Teff(LH17) - Teff(VOSA)) = 92.9 K; std = 132.4 K

    • BT-Settl CIFIST (Fig. 2)

      Mean(Teff(LH17) - Teff(VOSA)) = 86.3 K; std = 117.2 K

    Both models give consistent values for the effective temperature.

    Figure 1: Effective temperatures using BT-Settl. Correlation coefficient r = 0.95.

    Figure 2: Effective temperatures using BT-Settl CIFIST. Correlation coefficient r = 0.96.

    Metallicity

    • BT-Settl (Fig. 3)

      Mean(Metallicity(LH17) - Metallicity(VOSA)) = 0.18; std= 0.38

    BT-Settl does not provide good results for the metallicities.

    Figure 3: Metallicities using BT-Settl. Correlation coefficient r = 0.41.

    Surface gravity

    • BT-Settl (Fig. 4)

      Mean(log g(LH17) - log g(VOSA)) = 0.05; std= 0.61

    • BT-Settl CIFIST (Fig. 5)

      Mean(log g(LH17) - log g(VOSA)) = -0.48; std = 0.35

    Surface gravities provided by VOSA are not consistent with the values given in the paper. Using BT-Settl we obtain higher values for stars with the lowest gravities in LH17 and lower values for the stars with highest gravities (see Fig. 4). On the other hand, this does not happen using BT-Settl CIFIST but we obtain significantly higher values.

    Figure 4: Surface gravities using BT-Settl. Correlation coefficient r = -0.70.

    Figure 5: Surface gravities using BT-Settl CIFIST. Correlation coefficient r = -0.11.

    Radii and masses

    VOSA computes two stellar radii from two different equations: $$ M_d = (R_1 /D)$$ $$ L_{\rm bol} = 4\pi R_2^2 \ \sigma \ T_{\rm eff}^4$$

    where M d is the proportionality factor used to fit the model to the observations, D is the distance and $\sigma$ is the Stephan-Boltzmann constant.

    From $R_1$ and $R_2$ , VOSA provides also stellar masses by applying: $$ g = \frac{GM}{R^2}$$

    Since the surface gravities provided by VOSA do not agree with those given in the paper, we do not expect consistent masses either. In any case, we performed for the masses the same analysis as for the radii and will derive proper masses from the HR diagram.

    • BT-Settl (Figs. 6 and 7)
      • Mean(Radius(LH17) - Radius1(VOSA)) = -0.007; std = 0.033
      • Mean(Radius(LH17) - Radius2(VOSA)) = -0.003; std = 0.032
      • Mean(Mass(LH17) - Mass1(VOSA)) = -0.76; std= 1.59
      • Mean(Mass(LH17) - Mass2(VOSA) = -0.74; std = 1.56
    • BT-Settl CIFIST (Figs. 8 and 9)
      • Mean(Radius(LH17) - Radius1(VOSA)) = -0.003; std = 0.035
      • Mean(Radius(LH17) - Radius2(VOSA)) = -0.002; std = 0.036
      • Mean(Mass(LH17) - Mass1(VOSA)) = -1.69; std = 1.56
      • Mean(Mass(LH17) - Mass2(VOSA) = -1.68; std = 1.56

    There are not significant differences between the radii derived using BT- Settl or BT-Settl CIFIST models. Similar radii are obtained from Eqs. 1 and 2 and both are in very good agreement with the values derived by LH17.

    On the contrary, masses are not consistent with the masses expected for cool dwarfs and, hence, do not agree with those given in the paper, as expected from the log g values obtained with VOSA.

    Figure 6: Radii using BT-Settl. Correlation coefficient r = 0.97. Similar plots are obtained for the radii derived from Eq. 2.

    Figure 7: Masses using BT-Settl. Correlation coefficient r = 0.58. Similar plots are obtained for the masses derived from the radii calculated using Eq. 2.

    Figure 8: Radii using BT-Settl CIFIST. Correlation coefficient r = 0.97. Similar plots are obtained for the radii derived from Eq. 2.

    Figure 9: Masses using BT-Settl CIFIST. Correlation coefficient r = 0.65. Similar plots are obtained for the masses derived from the radii calculated using Eq. 2.

    Masses from HRD

    • BT-Settl (Fig. 10)

      Mean(Mass(LH17) - Mass(VOSA)) = 0.07; std = 0.06

      Two K dwarfs lie outside the area covered by the isochrone. With a few exceptions, we found good agreement between values for the thirteen remaining dwarfs.

    • BT-Settl CIFIST (Fig. 11)

      Mean(Mass(LH17) - Mass(VOSA)) = 0.08; std = 0.08

      In this case, only one K dwarf lies outside the area covered by the isochrone. The agreement with the masses in LH17 is worse using BHAC isochrones.


    Figure 10: Masses using BT-Settl isochrones. Correlation coefficient r = 0.93.

    Figure 11: Masses using BHAC isochrones. Correlation coefficient r = 0.85.

    Comparison with 48-Carmencita stars

    Date of this test: 2017/09/22 (by Miriam Cortés Contreras)

    (Download this test in pdf)

    Summary

    We compare the effective temperatures and luminosities derived by Carlos Cifuentes San Román (Master thesis, Sept. 2017, Universidad Complutense de Madrid; hereafter CCSR), and the effective temperatures from Passeger et al. in prep. (hereafter Pass17) with the fit results obtained with VOSA.

    • Effective temperatures

      VOSA provides effective temperatures using BT-Settl models in agreement with the estimated values of CCSR within 200 K. The comparison with the effective temperatures computed by Pass17 results in a higher dispersion. This differences are explained by the differences among CCSR's and Pass17's temperatures (the relation between them gives a correlation coefficient of r=0.88).

    • Luminosities

      Excellent agreement between the bolometric luminosities provided by VOSA and CCSR's.

    Sample and input parameters

    • CCSR
      • Effective temperatures estimation for 48 M dwarfs from their spectral types and low-resolution model spectra.
      • Luminosity determination for 48 M dwarfs given the magnitudes (u) B g V R r i J H K W1 W2 W3 W4 (u only used when available) performing numerical integration via Simpson's rule and Trapezoidal rule.
        • Up to 16 photometric passbands in the range 154 to 22088 nm.W.
        • Spectral types of the sample: M0 V -- M7.0 V.
        • 2600 < Teff < 4100 K.
        • 0.0007 < L < 0.1162 Lsun.
    • Pass17
      • Effective temperatures for 30 M dwarfs of the previous sample derived using high-resolution spectra taken with FEROS at the 2.2 m of the European Southern Observatory (La Silla, Chile), CAFE and CARMENES at the 2.2 m and 3.5 m telescopes in Calar Alto (Almería, Spain), and HRS at the 9.2 m HET (Texas).
      • 230 < Teff < 4169 K.
    • SED building using VOSA
      • Photometric SED built using photometry from GALEX, Stromgren, Johnson, SDSS, TYCHO, APASS, Gaia, DENIS, 2MASS, UKIDSS, VISTA, WISE, MSX, IRC and IRAS retrieved from VO services.
      • Model fit using BT-Settl (log{g}: 4.0 - 6.0; [M/H]: -0.5 - 0.5, Teff: 2300 - 5200 K)

    Parameters determination

    Of the 48 stars in this study, five have not enough photometric points retrieved by VOSA for the fit.

    • Effective temperatures

      To give an idea of the temperatures used for the analysis, the difference between them has a mean value of 58 K and a standard deviation of 111 K.

      • CCSR:

        Mean(Teff (CCSR) - Teff (VOSA)) = -7 K; std = 210 K

        Effective temperatures provided by VOSA are in agreement with those derived by CCSR with one exception which effective temperature is 1000 K higher than estimated by CCSR. Fig. 1.

        Figure 1: Comparison of CCSR's effective temperatures. Correlation coefficient r=0.87 (r=0.93 excluding the one outlier).
      • Pass17

        Mean(Teff (Pass17) - Teff (VOSA)) = -21 K; std = 334 K

        In this case, the concordance between temperatures is slightly worse, but also consistent. On average, VOSA provides higher values. Fig. 2.

        Figure 2: Comparison of Pass17's effective temperatures. Correlation coefficient r=0.67 (r=0.84 excluding the one outlier).
    • Luminosity

      In CCSR, luminosities were derived from two different approaches: via Simpson's rule and Trapezoidal rule. The difference between them has a mean value of 0.00008 Lsun and, therefore, the comparison will be carried out using the luminosities obtained via Trapezoidal rule. The comparison with those obtained via Simpson's rule would be analogue.

      Mean(L (CCSR) - L(VOSA)) = -0.002 Lsun, std= 0.004Lsun.

      The estimated luminosities are in very good agreement. Fig. 3.

      Figure 3: Luminosities comparison. Correlation coefficient r=0.99.

      Comparison with Rajpurohit et al. 2017

      Date of this test: 2017/09/21 (by Miriam Cortés Contreras)

      (Download this test in pdf)

      Summary

      We compare the results in Rajpurohit et al. 2017, arXiv170806211R (hereafter Ra17) with the fit results obtained with VOSA.

      • Effective temperatures

        Efective temperatures computed by VOSA are in agreement with those given by Rajpurohit et al. (2017) in the studied range from 3000 to 4000 K, with some dispersion towards higher values between 3100 and 3300 K. On average, temperatures provided by VOSA are systematically lower by less than 100 K and standard deviations are below 150 K for both BT-Settl and CIFIST models.

      • Surface gravities, metallicities

        Metallicities and surface gravities provided by VOSA are not reliable due to the minor contribution of these parameters to the SED shape.

      Sample and input parameters

      • Rajpurohit et al. 2017
        • Parameter determination for 45 M dwarfs using spectral synthesis employing BT-Settl models and high-resolution spectra taken with APOGEE on the Sloan 2.5 m Telescope at Apache Point Observatory in the H band:
          • H band (1.51 - 1.7 μm)
          • R ~ 22 500
        • Stellar properties:
          • Spectral types: M1.0 - M8.0 V
          • 3100 < Teff [K] < 3900 (± 100 K)
          • -0.50 < [Fe/H] < +0.50 with errors between 0.03 and 0.11.
          • 4 < logg [cm s2] < 5.5 with errors between 0.2 and 0.5.
      • SED building using VOSA
        • Photometric SED built using photometry from GALEX, Johnson, SDSS, APASS, Gaia, IPHAS, DENIS, UKIDSS, 2MASS, WISE and AKARI, retrieved from VO services.
        • Model fit using BT-Settl (logg: 4 - 5.5, [Fe/H]: -0.5 - 0.5, Teff:3000 - 4000 K).
        • Model fit using BT-Settl CIFIST (logg: 4 - 5.5, [M/H] = 0, Teff:3000-4000 K).

      Parameters determination

      We performed this analysis using BT-Settl models and used the more recent BT-Settl CIFIST models for comparison. Of the 45 M dwarfs of the analysis, only four had parallactic distances retrieved from VO services and another six had not enough photometric data for the fit.

      • Effective Temperatures
        • BT-Settl (Fig. 1)

          Mean(Teff (Ra17) - Teff (VOSA)) = 20.5 K; std = 111.4 K

        • BT-Settl CIFIST (Fig. 2)

          Mean(Teff (Ra17) - Teff (VOSA)) = 18.0 K; std = 110.6 K

        Both models provide quite similar values for the effective temperatures and are overall consistent within the errorbars with those given in Rajpurojit et al. (2017).

        Figure 1: Effective temperatures using BT-Settl. Correlation coefficient r=0.85.
        Figure 2: Effective temperatures using BT-Settl CIFIST. Correlation coefficient r=0.84.
      • Metallicity
        • BT-Settl (Fig. 3)

          Mean(Metallicity(Ra17) - Metallicity(VOSA)) = -0.19; std= 0.41

        No good determination of the metallicities using VOSA. On average, metallicities obtained using BT-Settl models differ with the values given by Rajpurohit et al. (2017) by more than 7σ.

        Figure 3: Metallicities using BT-Settl. Correlation coefficient r=0.25.
      • Surface gravity
        • BT-Settl (Fig. 4)

          Mean(logg (Ra17) - logg (VOSA)) = 0.36; std= 0.65

        • BT-Settl CIFIST (Fig. 5)

          Mean(logg (Ra17) - logg (VOSA)) = 0.29; std = 0.56

        The surface gravities given by VOSA strongly differ with those given by Rajpurohit et al. (2017) for near half of the analyzed sample. Hence, these values are not trustworthy.

        Figure 4: Surface gravities using BT-Settl. Correlation coefficient r=-0.22.
        Figure 5: Surface gravities using BT-Settl CIFIST. Correlation coefficient r=-0.29.