It is important that the SSPP be able to identify situations where the quoted
atmospheric parameters may be in doubt, or simply to make the user away where
possible anomalies might be found in the spectra of a given star. We have
designed a number of flags which serve this purpose.
of SSPP Flags
|n || All appears normal |
|D || Likely white dwarf |
|d || Likely sdO or sdB |
|H || Hot star with Teff > 10,000 K|
|h || Helium line detected, possibly very hot star|
|l || Likely solar abundance, late-type star|
|E || Emission lines in spectrum |
|S || Sky spectrum |
|V || No radial velocity information available|
|N || Noisy spectrum at extrema |
|C || The photometric g-r color may be incorrect |
|B || Unexpected Hα line strength predicted from Hδ
|G || Strong G-band feature |
|g || Mild G-band feature |
There are two primary categories of flags -- critical flags and cautionary
flags. Critical flags are discussed below. When a critical flag is
raised, the SSPP is set to either ignore the determinations of atmospheric
parameters for a given source, or it is forced (in the case of the color flag
described below) to take steps that differ from
normal processing in an attempt to rescue this information.
Obviously, even when
information is salvaged, the presence of a critical flag means the user must be
aware that special steps have been taken, and the reported estimated parameters
must be viewed with this knowledge in mind.
The second category of flags are the
cautionary flags, which are provided for user consideration, but are not
necessarily cause for undue concern. Indeed, sometimes these flags are raised
when all is in fact OK, but the flag has been raised due to a peculiarity
spectrum that is relatively harmless, and which will not unduly influence the
determinations of atmospheric parameters. The user should nevertheless be aware
of the existence of these flags.
The flags are combined into a single set of four letters, the meanings of which
are summarized in the table above, and described below in more detail.
are used in order to accommodate cases where more than one sort of flag is
The nominal condition for the four letter flag combination is `nnnn', which
indicates that the SSPP is satisfied that a given stellar spectrum (and its
reported g-r colors) has passed all of the tests that have been performed,
the stellar parameters should be considered as well determined.
The first letter in this combination is set to one of 10 different values:
D, d, H, h, l, E, S, V, and N. Their explanations follow:
- n: The letter n indicates nominal.
- D: The letter D indicates that a comparison of the breadth of the
Hδ line at 20% below its continuum, D0.2, and the line
depth below the
continuum, Rc, relative to their expected relationship for
provided below, does not apply. The expected relationship is given by:
Rc = -0.009503 + 0.027740D0.2 -
0.000590D0.22 + 0.000006D0.23
If D0.2 is greater than 35.0 Å and the predicted
Rc from the above relationship is less than the measured value,
then the star is most likely a white dwarf. This is a critical flag.
- d: This flag is raised if D0.2 is less than 35.0 Å
predicted Rc from above is less than the measured value. In
this case, the star is most likely a sdO or sdB star. This is a
- H: This flag is raised when the estimated Teff from
the SSPP is
greater than 10,000K, and is meant to indicate a hot star. This is a critical
- h: This flag is raised if the estimated Teff from the
SSPP is greater than 8,000K, and either of the line indices of He I
(at 4026.2 Å) or He I (at 4471.7 Å) is greater than 1.0 Å.
This indicates that the star is likely to be a hot star. This is a
- l: This flag is raised if the SSPP judges the star to have a high
likelihood of being a late type star (generally late K, M, or later
spectral type), beyond the ability of the present pipeline to
determine acceptable atmospheric parameter estimates. The condition
used for raising the l flag is that the Na line (5892.9 Å)
index, as measured over a 24 Å band centered on this feature, is
larger than 10 Å, and the g-r color is greater than 0.80. This
is a critical flag.
- E: This flag is raised if significant emission lines are detected
in a spectrum. This is a critical flag.
- S: This flag is raised if the spectrum (according to the header
is a night sky spectrum. This is a critical flag.
- V: This flag is raised when an adequate radial velocity could not
be found for a given spectrum. This is a critical flag.
- N: This flag is raised if the spectrum is considered noisy at the extremes
of the wavelength range (e.g., around Ca II K and the Ca II triplet).
This is a cautionary flag.
The flags that are used to fill out the remaining three positions of the four
letter flag combination are C, B, G, or g, as described below:
- C: This flag is raised if the SSPP is concerned that the reported
g-r color is incorrect. As mentioned in
Lee et al 2007, we calculate
three estimates of
predicted g-r colors.
For each of these three predicted colors, we find the one which is closest to
the reported g-r color based on the photometry. If the difference between the
reported color and the closest predicted color is larger than 0.2 magnitudes,
the color flag is raised. The SSPP is set up to proceed with its calculations
atmospheric parameters using the predicted g-r color. This flag is always
found in the second position of the combination flag parameters. This is a
- B: This flag is raised if the SSPP is concerned that there exists a
between the strength of the predicted Hα line index HA24, based on the
measured Hδ line index, HD24. For the great majority of normal
stars, the predicted value of the H\alpha line index is found to be HA24 =
2.737 + 0.775HD24. For stars with significant HA24 and HD24 measurements
(which we take to mean that the values of these indices exceed zero by
2σ, where σ is the error in the measured line index), if the
difference between the predicted HA24 line index and the measured HA24 index
is larger than 2.5 Å, then the B flag is raised. This flag is always found
in the third position of the combination flag parameters. This is a cautionary
- G or g: This flag is raised if the SSPP suggests that the star may
strong (G) or mild (g) CH G-band (around 4,300 Å), relative to
expectation for normal stars. This flag is always found in the fourth
position of the combination flag parameters. This is a cautionary flag.