DRAFT
2025-01-10 20:29:40
Type: Object/s-Discovery/Classification
Bibcode: 2025TNSAN..12....1S
Discovery of a Likely Luminous Blue Variable in HST/WFC3 Imaging of NGC 4414
Authors: Huei Sears (Rutgers, The State University of New Jersey), Or Graur (University of Portsmouth), Saurabh Jha (Rutgers, The State University of New Jersey), Conor Larison (Rutgers, The State University of New Jersey), Nathan Smith (The University of Arizona), Jay Strader (Michigan State University)
Keywords: Variable Star

We report the discovery of a likely luminous blue variable (LBV) in the galaxy NGC 4414 at RA and Dec 12:26:26.275, +31:13:24.01 (J2000).  The source brightened substantially in HST/WFC3 F555W imaging on MJD 60451 and is detected at fainter magnitudes in earlier F555W imaging on MJD 59260, 59886, 60041, 60076, 60144, and 60316. The source is also detected in WFC3 F438W imaging on MJD 59886 and in WFC3 F625W imaging on MJD 60144. We perform PSF photometry on the source in all mentioned HST images using dolphot (Dolphin, 2000, 2016) and find magnitudes (Vega) as follows:
 

MJD 59260  F555W = 22.978 +/- 0.017 mag

MJD 59886  F555W = 22.959 +/- 0.018 mag

MJD 59886  F438W = 22.755 +/- 0.018 mag

MJD 60041  F555W = 21.934 +/- 0.008 mag

MJD 60076  F555W = 22.627 +/- 0.009 mag

MJD 60144  F555W = 21.948 +/- 0.008 mag

MJD 60144  F625W = 21.096 +/- 0.006 mag

MJD 60316  F555W = 23.009 +/- 0.009 mag

MJD 60451  F555W = 18.744 +/- 0.001 mag
 

The MJD 59886 F438W - F555W color is -0.20 mag and the MJD 60144 F555W - F625W color is +0.85 mag. Magnitude uncertainties are statistical only and likely underestimated. Forced photometry at the location of the source in ATLAS and ZTF observations seems to show variability roughly consistent with the HST observations, however the proximity of the source to the center of the galaxy could lead to spurious detections at epochs with poor observing conditions. Further HST F555W observations of this field are planned.

In a TNS search for sources at this location, no sources come up within a 5’’ radius, however a SIMBAD searchin a similar radius shows the C4 molecular cloud identified in Sakamoto 1996.  The color evolution of the source (blue at quiescence and red at outburst) is consistent with an LBV, as is the pre-outburst variability (Weis & Bomans, 2020). With a distance modulus for NGC 4414 of 31.41 mag (Turner et al., 1998), the F555W outburst magnitude converts to an absolute magnitude of ~ -12.7 mag, without accounting for host extinction.  This would be bright for an LBV outburst, though not unprecedented (Smith et al., 2011).

Show current TNS values
Catalog Name Reported RA Reported DEC Reported Obj-Type Reported Redshift Host Name Host Redshift Remarks TNS RA TNS DEC TNS Obj-Type TNS Redshift
TNS 2024agob 12:26:26.280 +31:13:24.01 LBV 0.002388 NGC 4414 0.002388 12:26:26.280 +31:13:24.01

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