J/MNRAS/545/F2137 Third quadrant bright VPHAS+ photometry (Drew+, 2026)
Uniformly calibrated VPHAS+ photometry in the third quadrant of the
Galactic plane.
Drew J.E., Greimel R., Eisloeffel J., Raddi R., Wright N.J.
<Mon. Not. R. Astron. Soc. 545, staf2137 (2026)>
=2026MNRAS.545f2137D 2026MNRAS.545f2137D (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Galactic plane ; Photometry, ugriz ;
Photometry, H-alpha
Keywords: Galactic plane - Surveys - Photometry, ugriz - Photometry, H-alpha -
Stars, early-type - Stars, emission - Stars, luminous - YSOs -
Extinction
Abstract:
The southern Galactic plane has been mapped at optical wavelengths and
at under 1-arcsec angular resolution by the VST Photometric Halpha
Survey of the Galactic plane and bulge (VPHAS+). Ahead of the release
of a uniform photometric calibration of the entire survey footprint,
we examine the properties of r<19 VPHAS+ point-source photometry in
the third Galactic quadrant. Our interim calibration in g, r and i is
compared with that of Pan-STARRS, DECaPS-2 and Skymapper, revealing
the need for small gri photometric offsets. Corrections to the Halpha
and u magnitude scales are determined via comparison with synthetic
photometry. VPHAS+ and its northern counterpart, IGAPS, are shown to
closely align across the celestial equator. Aided by Gaia DR3, SIMBAD,
and specialist catalogues, we explore selections of: A stars;
sub-luminous stars; intrinsically-red luminous stars; young stellar
objects; emission-line and OB stars. Attention is drawn to stellar
variability as a contaminant in selecting emission line objects via (r
- Halpha) excess. The (r-i, r-Halpha) plane appears better for
this selection than the alternative (g-i, r-Halpha) plane. Using A
stars to map extinction, we show that dust obscuration is greater at
negative Galactic latitudes. Like the dust, OB and emission line stars
are more frequent below the Galactic equator: at heliocentric
distances of up to ∼7kpc, these stars' distribution fit in with the
known warping of the Galactic plane. An overdensity of B stars,
several degrees across and potentially in the Outer Arm, is found
around (l,b) = (212.0, -0.6).
Description:
The catalogue contains uniformly-calibrated ugri and Halpha photometry
from the VPHAS+ survey for point sources brighter than r(AB)<19,
within the Galactic longitude range, ∼210<l<260 (coverage over the
-5<b<+5 survey band is complete from l=212.5). Corrected as
described in the paper, magnitudes are provided in both the AB and
Vega systems. The data per survey field were obtained in a 'blue'
observing block exposing in u, g and r (rb in the catalogue) at a
different epoch from the 'red' observing block covering r (rr in the
catalogue), i and H-alpha: as a result, the two r magnitudes, rb and
rr, are usually non-identical due to secular variation and/or
measurement error. The last three columns in the catalogue give SIMBAD
main identifier, object class and spectral type for the <1 percent of
sources with SIMBAD crossmatches.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
vphasq3b.dat 366 11421469 Photometric catalogue
--------------------------------------------------------------------------------
See also:
II/386 : VPHAS+ DR3 survey (Drew+, 2025)
Byte-by-byte Description of file: vphasq3b.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension (J2000.0) (RA)
11- 19 F9.5 deg DEdeg Declination (J2000.0) (DEC)
21- 29 F9.5 deg GLON Galactic longitude (l)
31- 39 F9.5 deg GLAT Galactic latitude (b)
41- 45 F5.3 --- mergedClass Band-merged morphological class
(mergedClass) (1)
47- 52 F6.3 mag imagAB i magnitude in the AB system (i_AB)
54- 59 F6.3 mag imagV i magnitude in the Vega system (i_V)
61- 68 F8.6 mag e_imagV Photometric uncertainty in i magnitude
(err_i)
70- 74 F5.3 --- Classi i morphological class (Class_i) (1)
76- 82 F7.3 --- Avconfi i confidence level (Avconfi)
84 I1 --- errbitsi i band cumulative warning flag
(errbits_i) (2)
86- 91 F6.3 mag HamagAB ?=- H-alpha magnitude in the AB system
(Ha_AB)
93- 98 F6.3 mag HamagV ?=- H-alpha magnitude in the Vega system
(Ha_V)
100-107 F8.6 mag e_HamagAB ?=- photometric uncertainty in H-alpha
magnitude (err_Ha)
109-113 F5.3 --- ClassHa ?=- H-alpha morphological class
(Class_Ha) (1)
115-121 F7.3 --- AvconfHa ?=- H-alpha confidence level (AvconfHa)
123-127 I5 --- errbitsHa ?=- H-alpha narrow band cumulative warning
flag (errbits_Ha) (2)
129-134 F6.3 mag rrmagAB Red-OB r band AB magnitude (rr_AB)
136-141 F6.3 mag rrmagV Red-OB r band Vega magnitude (rr_V)
143-150 F8.6 mag e_rrmagAB Photometric uncertainty in red-OB r
magnitude (err_rr)
152-156 F5.3 --- Classrr Red-OB r band morphological class (Class_rr)
158-165 F8.4 --- Avconfrr Red-OB r band confidence level (Avconfrr)
167 I1 --- errbitsrr Red-OB r band cumulative warning flag
(errbits_rr) (2)
169-174 F6.3 mag rbmagAB Blue-OB r band AB magnitude (rb_AB)
176-181 F6.3 mag rbmagV Blue-OB r band Vega magnitude (rb_V)
183-190 F8.6 mag e_rbmagAB Photometric uncertainty in blue-OB
r magnitude (err_rb)
192-196 F5.3 --- Class_rb Blue-OB r band morphological class
(Class_rb) (1)
198-205 F8.4 --- Avconfrb Blue-OB r band confidence level (Avconfrb)
207 I1 --- errbitsrb Blue-OB r band cumulative warning flag
(errbits_rb) (2)
209-214 F6.3 mag gmagAB g band AB magnitude (g_AB)
216-221 F6.3 mag gmagV g band Vega magnitude (g_V)
223-230 F8.6 mag e_gmagAB Photometric uncertainty in g magnitude
(err_g)
232-236 F5.3 --- Classg g morphological class (Class_g) (1)
238-245 F8.4 --- Avconfg g band confidence level (Avconfg)
247 I1 --- errbitsg g band cumulative warning flag
(errbits_g) (2)
249-254 F6.3 mag umagAB ?=- u band AB magnitude (u_AB)
256-261 F6.3 mag umagV ?=- u band Vega magnitude (u_V)
263-270 F8.6 mag e_umagAB ?=- photometric uncertainty in u magnitude
(err_u)
272-276 F5.3 --- Classu ?=- u morphological class (Class_u) (1)
278-285 F8.4 --- Avconfu ?=- u band confidence level (Avconfu)
287-291 I5 --- errbitsu ?=- u band cumulative warning flag
(errbits_u) (2)
293-329 A37 --- MainId SIMBAD main identifier of object (main_id)
331-353 A23 --- MainType SIMBAD main object class (main_type)
355-366 A12 --- SpType SIMBAD spectral type (sp_type)
--------------------------------------------------------------------------------
Note (1): morphological class is <2.5 for objects that may be regarded as
star-like.
Note (2): Flag as:
0 = indicates a source with no problems
2 = indicates an object that is the brighter component in a ded source
>2 = flags indicate increasingly unreliable measurements, and appear
against some H-alpha and u detections
--------------------------------------------------------------------------------
Acknowledgements:
Janet Drew, j.drew(at)ucl.ac.uk
(End) Janet Drew [University College London], Patricia Vannier [CDS] 04-Feb-2026