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Modelling brightness of variable stars #4208

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Modelling brightness of variable stars #4208

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262a15b
add initial support to display variable brightness for variable stars
henrysky Mar 14, 2025
6bd6877
improvement
henrysky Mar 29, 2025
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25 changes: 25 additions & 0 deletions src/core/modules/Star.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -446,6 +446,31 @@ struct Star
pmdec = sky_orbit_vel.dot(q2) * 1000.;
StelUtils::rectToSphe(&ra, &dec, v);
}

inline void getVarStarOffset(double epoch, double &offset) const // get brightness offset for variable stars (not actual brightness)
{
StarId star_id = (getGaia() == 0) ? getHip() : getGaia();
double period = StarMgr::getGcvsPeriod(star_id) / 365.25;
if (period <=0.) // not a variable star
return;
double dyrs = (epoch - STAR_CATALOG_JDEPOCH) / 365.25;
double min1mag = StarMgr::getGcvsMinMagnitude(star_id) * 1000.;
double maxmag = StarMgr::getGcvsMaxMagnitude(star_id) * 1000.;
QString name = StarMgr::getGcvsVariabilityType(star_id);
if (!name.isEmpty())
qDebug() << "Star " << name << " has period " << period << " days, min1mag " << min1mag << ", maxmag " << maxmag;
double epoch_offset = (StarMgr::getGcvsEpoch(star_id) - STAR_CATALOG_JDEPOCH) / 365.25;
double phase = fmod(dyrs - epoch_offset, period) / period;

if (period && min1mag && maxmag && min1mag > maxmag)
{
double amplitude = (min1mag - maxmag) / 2.;
if (phase < 0.0)
phase += 1.0;
// sine wave
offset = amplitude * sin(2. * M_PI * phase);
}
}
};

struct Star1 : public Star<Star1>
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12 changes: 9 additions & 3 deletions src/core/modules/StarWrapper.cpp
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Expand Up @@ -303,7 +303,9 @@ QString StarWrapper1::getInfoString(const StelCore *core, const InfoStringGroup&
{
magOffset = 5.f * log10(s->getPlx()/Plx);
}
oss << getMagnitudeInfoString(core, flags, 2, magOffset);
double variable_magoffset = 0.0;
s->getVarStarOffset(core->getJDE(), variable_magoffset);
oss << getMagnitudeInfoString(core, flags, 2, magOffset + variable_magoffset / 1000.);

// should use Plx from getPlx because Plx can change with time, but not absolute magnitude
if ((flags&AbsoluteMagnitude) && s->getPlx())
Expand Down Expand Up @@ -658,7 +660,9 @@ QString StarWrapper2::getInfoString(const StelCore *core, const InfoStringGroup&
oss << QString("%1: <b>%2</b>").arg(q_("Type"), objectTypeI18nStr) << "<br />";
}

oss << getMagnitudeInfoString(core, flags, 2);
double variable_magoffset = 0.0;
s->getVarStarOffset(core->getJDE(), variable_magoffset);
oss << getMagnitudeInfoString(core, flags, 2, variable_magoffset / 1000.);

double RA, DEC, pmra, pmdec, Plx, RadialVel;
double PlxErr = s->getPlxErr();
Expand Down Expand Up @@ -884,7 +888,9 @@ QString StarWrapper3::getInfoString(const StelCore *core, const InfoStringGroup&
oss << QString("%1: <b>%2</b>").arg(q_("Type"), objectTypeI18nStr) << "<br />";
}

oss << getMagnitudeInfoString(core, flags, 2);
double variable_magoffset = 0.0;
s->getVarStarOffset(core->getJDE(), variable_magoffset);
oss << getMagnitudeInfoString(core, flags, 2, variable_magoffset / 1000.);

if (flags&Extra)
{
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5 changes: 5 additions & 0 deletions src/core/modules/ZoneArray.cpp
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Expand Up @@ -487,6 +487,11 @@ void SpecialZoneArray<Star>::draw(StelPainter* sPainter, int index, bool isInsid
Vec3d u = (r * (1. + pmr0 * dyrs) + pmvec0 * dyrs) * f;
v.set(u[0], u[1], u[2]);
}
// take variable star brightness delta into account
double variable_magoffset = 0.0;
s->getVarStarOffset(core->getJDE(), variable_magoffset);
starMag += variable_magoffset;

// recompute magIndex with the new magnitude
magIndex = static_cast<int>((starMag - (mag_min - 7000.)) * 0.02); // 1 / (50 milli-mag)

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